Enhancement: mail message preprocessor for gpg encrypted mails (#7456)

---------

Co-authored-by: shamoon <4887959+shamoon@users.noreply.github.com>

diff --git a/Dockerfile b/Dockerfile
index 2a9d7b306779e0a7cace41a607a833b7ef898f66..4ef558712cef487bb1c44cf42aa79e6d3b19f2bd 100644 (file)
--- a/Dockerfile
+++ b/Dockerfile
@@ -275,6 +275,8 @@ RUN set -eux \
     && mkdir --parents --verbose /usr/src/paperless/media \
     && mkdir --parents --verbose /usr/src/paperless/consume \
     && mkdir --parents --verbose /usr/src/paperless/export \
+  && echo "Creating gnupg directory" \
+    && mkdir -m700 --verbose /usr/src/paperless/.gnupg \
   && echo "Adjusting all permissions" \
     && chown --from root:root --changes --recursive paperless:paperless /usr/src/paperless \
   && echo "Collecting static files" \

diff --git a/docs/advanced_usage.md b/docs/advanced_usage.md
index 5488659a250bd7682fb01c97b37028ffa131c4a9..fe7099e2d966c23986bece7b491c86ada3038cec 100644 (file)
--- a/docs/advanced_usage.md
+++ b/docs/advanced_usage.md
@@ -690,3 +690,57 @@ More details about configuration option for various providers can be found in th
 
 Once external auth is set up, 'regular' login can be disabled with the [PAPERLESS_DISABLE_REGULAR_LOGIN](configuration.md#PAPERLESS_DISABLE_REGULAR_LOGIN) setting and / or users can be automatically
 redirected with the [PAPERLESS_REDIRECT_LOGIN_TO_SSO](configuration.md#PAPERLESS_REDIRECT_LOGIN_TO_SSO) setting.
+
+## Decryption of encrypted emails before consumption {#gpg-decryptor}
+
+Paperless-ngx can be configured to decrypt gpg encrypted emails before consumption.
+
+### Requirements
+
+You need a recent version of `gpg-agent >= 2.1.1` installed on your host.
+Your host needs to be setup for decrypting your emails via `gpg-agent`, see this [tutorial](https://www.digitalocean.com/community/tutorials/how-to-use-gpg-to-encrypt-and-sign-messages#encrypt-and-decrypt-messages-with-gpg) for instance.
+Test your setup and make sure that you can encrypt and decrypt files using your key
+
+```
+gpg --encrypt --armor -r person@email.com name_of_file
+gpg --decrypt name_of_file.asc
+```
+
+### Setup
+
+First, enable the [PAPERLESS_GPG_DECRYPTOR environment variable](configuration.md#PAPERLESS_GPG_DECRYPTOR).
+
+Then determine your local `gpg-agent.extra` socket by invoking
+
+```
+gpgconf --list-dir agent-extra-socket
+```
+
+on your host. A possible output is `~/.gnupg/S.gpg-agent.extra`.
+Also find the location of your public keyring.
+
+If using docker, you'll need to add the following volume mounts to your `docker-compose.yml` file:
+
+```yaml
+webserver:
+  volumes:
+    - /home/user/.gnupg/pubring.gpg:/usr/src/paperless/.gnupg/pubring.gpg
+    - <path to gpg-agent.extra socket>:/usr/src/paperless/.gnupg/S.gpg-agent
+```
+
+For a 'bare-metal' installation no further configuration is necessary. If you
+want to use a separate `GNUPG_HOME`, you can do so by configuring the [PAPERLESS_EMAIL_GNUPG_HOME environment variable](configuration.md#PAPERLESS_EMAIL_GNUPG_HOME).
+
+### Troubleshooting
+
+- Make sure, that `gpg-agent` is running on your host machine
+- Make sure, that encryption and decryption works from inside the container using the `gpg` commands from above.
+- Check that all files in `/usr/src/paperless/.gnupg` have correct permissions
+
+```shell
+paperless@9da1865df327:~/.gnupg$ ls -al
+drwx------ 1 paperless paperless   4096 Aug 18 17:52 .
+drwxr-xr-x 1 paperless paperless   4096 Aug 18 17:52 ..
+srw------- 1 paperless paperless      0 Aug 18 17:22 S.gpg-agent
+-rw------- 1 paperless paperless 147940 Jul 24 10:23 pubring.gpg
+```

diff --git a/docs/configuration.md b/docs/configuration.md
index e719e043ddf82e50eac99379ac524c96201be934..7172afcb3c513556eedab3669addb21d2a83876b 100644 (file)
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -1149,6 +1149,18 @@ within your documents.
     second, and year last order. Characters D, M, or Y can be shuffled
     to meet the required order.
 
+#### [`PAPERLESS_GPG_DECRYPTOR=<bool>`](#PAPERLESS_GPG_DECRYPTOR) {#PAPERLESS_GPG_DECRYPTOR}
+
+: Enable or disable the GPG decryptor for encrypted emails. See [GPG Decryptor](advanced_usage.md#gpg-decryptor) for more information.
+
+    Defaults to false.
+
+#### [`PAPERLESS_EMAIL_GNUPG_HOME=<str>`](#PAPERLESS_EMAIL_GNUPG_HOME) {#PAPERLESS_EMAIL_GNUPG_HOME}
+
+: Optional, sets the `GNUPG_HOME` path to use with GPG decryptor for encrypted emails. See [GPG Decryptor](advanced_usage.md#gpg-decryptor) for more information. If not set, defaults to the default `GNUPG_HOME` path.
+
+    Defaults to <not set>.
+
 ### Polling {#polling}
 
 #### [`PAPERLESS_CONSUMER_POLLING=<num>`](#PAPERLESS_CONSUMER_POLLING) {#PAPERLESS_CONSUMER_POLLING}

diff --git a/src/paperless/settings.py b/src/paperless/settings.py
index 000904aef11d913fc559a090980f745dc8c50fcc..27c609e8d5025f037c7fce19be7e0ce9ead617c1 100644 (file)
--- a/src/paperless/settings.py
+++ b/src/paperless/settings.py
@@ -1171,6 +1171,15 @@ if DEBUG:  # pragma: no cover
     EMAIL_BACKEND = "django.core.mail.backends.filebased.EmailBackend"
     EMAIL_FILE_PATH = BASE_DIR / "sent_emails"
 
+###############################################################################
+# Email Preprocessors                                                         #
+###############################################################################
+
+EMAIL_GNUPG_HOME: Final[Optional[str]] = os.getenv("PAPERLESS_EMAIL_GNUPG_HOME")
+EMAIL_ENABLE_GPG_DECRYPTOR: Final[bool] = __get_boolean(
+    "PAPERLESS_ENABLE_GPG_DECRYPTOR",
+)
+
 
 ###############################################################################
 # Soft Delete

diff --git a/src/paperless_mail/mail.py b/src/paperless_mail/mail.py
index 83771dbf52bd44149b774a8c30ec71e9a1ae8dba..92c4718454391a10a7295b96a3bc35647ab09f79 100644 (file)
--- a/src/paperless_mail/mail.py
+++ b/src/paperless_mail/mail.py
@@ -43,6 +43,8 @@ from documents.tasks import consume_file
 from paperless_mail.models import MailAccount
 from paperless_mail.models import MailRule
 from paperless_mail.models import ProcessedMail
+from paperless_mail.preprocessor import MailMessageDecryptor
+from paperless_mail.preprocessor import MailMessagePreprocessor
 
 # Apple Mail sets multiple IMAP KEYWORD and the general "\Flagged" FLAG
 # imaplib => conn.fetch(b"<message_id>", "FLAGS")
@@ -426,9 +428,30 @@ class MailAccountHandler(LoggingMixin):
 
     logging_name = "paperless_mail"
 
+    _message_preprocessor_types: list[type[MailMessagePreprocessor]] = [
+        MailMessageDecryptor,
+    ]
+
     def __init__(self) -> None:
         super().__init__()
         self.renew_logging_group()
+        self._init_preprocessors()
+
+    def _init_preprocessors(self):
+        self._message_preprocessors: list[MailMessagePreprocessor] = []
+        for preprocessor_type in self._message_preprocessor_types:
+            self._init_preprocessor(preprocessor_type)
+
+    def _init_preprocessor(self, preprocessor_type):
+        if preprocessor_type.able_to_run():
+            try:
+                self._message_preprocessors.append(preprocessor_type())
+            except Exception as e:
+                self.log.warning(
+                    f"Error while initializing preprocessor {preprocessor_type.NAME}: {e}",
+                )
+        else:
+            self.log.debug(f"Skipping mail preprocessor {preprocessor_type.NAME}")
 
     def _correspondent_from_name(self, name: str) -> Optional[Correspondent]:
         try:
@@ -535,6 +558,11 @@ class MailAccountHandler(LoggingMixin):
 
         return total_processed_files
 
+    def _preprocess_message(self, message: MailMessage):
+        for preprocessor in self._message_preprocessors:
+            message = preprocessor.run(message)
+        return message
+
     def _handle_mail_rule(
         self,
         M: MailBox,
@@ -613,6 +641,8 @@ class MailAccountHandler(LoggingMixin):
         return total_processed_files
 
     def _handle_message(self, message, rule: MailRule) -> int:
+        message = self._preprocess_message(message)
+
         processed_elements = 0
 
         # Skip Message handling when only attachments are to be processed but

diff --git a/src/paperless_mail/preprocessor.py b/src/paperless_mail/preprocessor.py
new file mode 100644 (file)
index 0000000..7e0c767
--- /dev/null
+++ b/src/paperless_mail/preprocessor.py
@@ -0,0 +1,103 @@
+import abc
+import os
+from email import message_from_bytes
+from email import policy
+from email.message import Message
+
+from django.conf import settings
+from gnupg import GPG
+from imap_tools import MailMessage
+
+from documents.loggers import LoggingMixin
+
+
+class MailMessagePreprocessor(abc.ABC):
+    """
+    Defines the interface for preprocessors that alter messages before they are handled in MailAccountHandler
+    """
+
+    NAME: str = "MailMessagePreprocessor"
+
+    @staticmethod
+    @abc.abstractmethod
+    def able_to_run() -> bool:
+        """
+        Return True if the conditions are met for the preprocessor to run, False otherwise
+
+        If False, run(message) will not be called
+        """
+
+    @abc.abstractmethod
+    def run(self, message: MailMessage) -> MailMessage:
+        """
+        Performs the actual preprocessing task
+        """
+
+
+class MailMessageDecryptor(MailMessagePreprocessor, LoggingMixin):
+    logging_name = "paperless_mail_message_decryptor"
+
+    NAME = "MailMessageDecryptor"
+
+    def __init__(self):
+        super().__init__()
+        self.renew_logging_group()
+        self._gpg = GPG(gnupghome=settings.EMAIL_GNUPG_HOME)
+
+    @staticmethod
+    def able_to_run() -> bool:
+        if not settings.EMAIL_ENABLE_GPG_DECRYPTOR:
+            return False
+        if settings.EMAIL_GNUPG_HOME is None:
+            return True
+        return os.path.isdir(settings.EMAIL_GNUPG_HOME)
+
+    def run(self, message: MailMessage) -> MailMessage:
+        if not hasattr(message, "obj"):
+            self.log.debug("Message does not have 'obj' attribute")
+            return message
+        if message.obj.get_content_type() != "multipart/encrypted":
+            self.log.debug("Message not encrypted. Keep unchanged")
+            return message
+
+        self.log.debug("Message is encrypted.")
+        email_message = self._to_email_message(message)
+        decrypted_raw_message = self._gpg.decrypt(email_message.as_string())
+
+        if not decrypted_raw_message.ok:
+            self.log.debug(
+                f"Message decryption failed with status message "
+                f"{decrypted_raw_message.status}",
+            )
+            raise Exception(
+                f"Decryption failed: {decrypted_raw_message.status}, {decrypted_raw_message.stderr}",
+            )
+        self.log.debug("Message decrypted successfully.")
+
+        decrypted_message = self._build_decrypted_message(
+            decrypted_raw_message,
+            email_message,
+        )
+
+        return MailMessage(
+            [(f"UID {message.uid}".encode(), decrypted_message.as_bytes())],
+        )
+
+    @staticmethod
+    def _to_email_message(message: MailMessage) -> Message:
+        email_message = message_from_bytes(
+            message.obj.as_bytes(),
+            policy=policy.default,
+        )
+        return email_message
+
+    @staticmethod
+    def _build_decrypted_message(decrypted_raw_message, email_message):
+        decrypted_message = message_from_bytes(
+            decrypted_raw_message.data,
+            policy=policy.default,
+        )
+        for header, value in email_message.items():
+            if not decrypted_message.get(header):
+                decrypted_message.add_header(header, value)
+        return decrypted_message

diff --git a/src/paperless_mail/tests/test_mail.py b/src/paperless_mail/tests/test_mail.py
index 0920f033c9a5aa71f6de9358a9a4241df64be634..d671021bfd8cb00d7886bab996465a4619fdd939 100644 (file)
--- a/src/paperless_mail/tests/test_mail.py
+++ b/src/paperless_mail/tests/test_mail.py
@@ -193,31 +193,10 @@ def fake_magic_from_buffer(buffer, mime=False):
         return "Some verbose file description"
 
 
-@mock.patch("paperless_mail.mail.magic.from_buffer", fake_magic_from_buffer)
-class TestMail(
-    DirectoriesMixin,
-    FileSystemAssertsMixin,
-    TestCase,
-):
-    def setUp(self):
+class MessageBuilder:
+    def __init__(self):
         self._used_uids = set()
 
-        self.bogus_mailbox = BogusMailBox()
-
-        patcher = mock.patch("paperless_mail.mail.MailBox")
-        m = patcher.start()
-        m.return_value = self.bogus_mailbox
-        self.addCleanup(patcher.stop)
-
-        patcher = mock.patch("paperless_mail.mail.queue_consumption_tasks")
-        self._queue_consumption_tasks_mock = patcher.start()
-        self.addCleanup(patcher.stop)
-
-        self.reset_bogus_mailbox()
-
-        self.mail_account_handler = MailAccountHandler()
-        super().setUp()
-
     def create_message(
         self,
         attachments: Union[int, list[_AttachmentDef]] = 1,
@@ -283,39 +262,132 @@ class TestMail(
 
         return imap_msg
 
-    def reset_bogus_mailbox(self):
-        self.bogus_mailbox.messages = []
-        self.bogus_mailbox.messages_spam = []
-        self.bogus_mailbox.messages.append(
-            self.create_message(
-                subject="Invoice 1",
-                from_="amazon@amazon.de",
-                to=["me@myselfandi.com", "helpdesk@mydomain.com"],
-                body="cables",
-                seen=True,
-                flagged=False,
-                processed=False,
-            ),
-        )
-        self.bogus_mailbox.messages.append(
-            self.create_message(
-                subject="Invoice 2",
-                body="from my favorite electronic store",
-                to=["invoices@mycompany.com"],
-                seen=False,
-                flagged=True,
-                processed=True,
-            ),
-        )
-        self.bogus_mailbox.messages.append(
-            self.create_message(
-                subject="Claim your $10M price now!",
-                from_="amazon@amazon-some-indian-site.org",
-                to="special@me.me",
-                seen=False,
-            ),
+
+def reset_bogus_mailbox(bogus_mailbox: BogusMailBox, message_builder: MessageBuilder):
+    bogus_mailbox.messages = []
+    bogus_mailbox.messages_spam = []
+    bogus_mailbox.messages.append(
+        message_builder.create_message(
+            subject="Invoice 1",
+            from_="amazon@amazon.de",
+            to=["me@myselfandi.com", "helpdesk@mydomain.com"],
+            body="cables",
+            seen=True,
+            flagged=False,
+            processed=False,
+        ),
+    )
+    bogus_mailbox.messages.append(
+        message_builder.create_message(
+            subject="Invoice 2",
+            body="from my favorite electronic store",
+            to=["invoices@mycompany.com"],
+            seen=False,
+            flagged=True,
+            processed=True,
+        ),
+    )
+    bogus_mailbox.messages.append(
+        message_builder.create_message(
+            subject="Claim your $10M price now!",
+            from_="amazon@amazon-some-indian-site.org",
+            to=["special@me.me"],
+            seen=False,
+        ),
+    )
+    bogus_mailbox.updateClient()
+
+
+class MailMocker(DirectoriesMixin, FileSystemAssertsMixin, TestCase):
+    def setUp(self):
+        self.bogus_mailbox = BogusMailBox()
+        self.messageBuilder = MessageBuilder()
+
+        reset_bogus_mailbox(self.bogus_mailbox, self.messageBuilder)
+
+        patcher = mock.patch("paperless_mail.mail.MailBox")
+        m = patcher.start()
+        m.return_value = self.bogus_mailbox
+        self.addCleanup(patcher.stop)
+
+        patcher = mock.patch("paperless_mail.mail.queue_consumption_tasks")
+        self._queue_consumption_tasks_mock = patcher.start()
+        self.addCleanup(patcher.stop)
+
+        super().setUp()
+
+    def assert_queue_consumption_tasks_call_args(
+        self,
+        expected_call_args: list[list[dict[str, str]]],
+    ):
+        """
+        Verifies that queue_consumption_tasks has been called with the expected arguments.
+
+        expected_call_args is the following format:
+
+        * List of calls to queue_consumption_tasks, called once per mail, where each element is:
+        * List of signatures for the consume_file task, where each element is:
+        * dictionary containing arguments that need to be present in the consume_file signature.
+
+        """
+
+        # assert number of calls to queue_consumption_tasks match
+        self.assertEqual(
+            len(self._queue_consumption_tasks_mock.call_args_list),
+            len(expected_call_args),
         )
-        self.bogus_mailbox.updateClient()
+
+        for (mock_args, mock_kwargs), expected_signatures in zip(
+            self._queue_consumption_tasks_mock.call_args_list,
+            expected_call_args,
+        ):
+            consume_tasks = mock_kwargs["consume_tasks"]
+
+            # assert number of consume_file tasks match
+            self.assertEqual(len(consume_tasks), len(expected_signatures))
+
+            for consume_task, expected_signature in zip(
+                consume_tasks,
+                expected_signatures,
+            ):
+                input_doc, overrides = consume_task.args
+
+                # assert the file exists
+                self.assertIsFile(input_doc.original_file)
+
+                # assert all expected arguments are present in the signature
+                for key, value in expected_signature.items():
+                    if key == "override_correspondent_id":
+                        self.assertEqual(overrides.correspondent_id, value)
+                    elif key == "override_filename":
+                        self.assertEqual(overrides.filename, value)
+                    elif key == "override_title":
+                        self.assertEqual(overrides.title, value)
+                    else:
+                        self.fail("No match for expected arg")
+
+    def apply_mail_actions(self):
+        """
+        Applies pending actions to mails by inspecting calls to the queue_consumption_tasks method.
+        """
+        for args, kwargs in self._queue_consumption_tasks_mock.call_args_list:
+            message = kwargs["message"]
+            rule = kwargs["rule"]
+            apply_mail_action([], rule.pk, message.uid, message.subject, message.date)
+
+
+@mock.patch("paperless_mail.mail.magic.from_buffer", fake_magic_from_buffer)
+class TestMail(
+    DirectoriesMixin,
+    FileSystemAssertsMixin,
+    TestCase,
+):
+    def setUp(self):
+        self.mailMocker = MailMocker()
+        self.mailMocker.setUp()
+        self.mail_account_handler = MailAccountHandler()
+
+        super().setUp()
 
     def test_get_correspondent(self):
         message = namedtuple("MailMessage", [])
@@ -399,7 +471,7 @@ class TestMail(
         self.assertEqual(handler._get_title(message, att, rule), None)
 
     def test_handle_message(self):
-        message = self.create_message(
+        message = self.mailMocker.messageBuilder.create_message(
             subject="the message title",
             from_="Myself",
             attachments=2,
@@ -416,9 +488,9 @@ class TestMail(
 
         self.assertEqual(result, 2)
 
-        self._queue_consumption_tasks_mock.assert_called()
+        self.mailMocker._queue_consumption_tasks_mock.assert_called()
 
-        self.assert_queue_consumption_tasks_call_args(
+        self.mailMocker.assert_queue_consumption_tasks_call_args(
             [
                 [
                     {"override_title": "file_0", "override_filename": "file_0.pdf"},
@@ -435,11 +507,11 @@ class TestMail(
 
         result = self.mail_account_handler._handle_message(message, rule)
 
-        self._queue_consumption_tasks_mock.assert_not_called()
+        self.mailMocker._queue_consumption_tasks_mock.assert_not_called()
         self.assertEqual(result, 0)
 
     def test_handle_unknown_mime_type(self):
-        message = self.create_message(
+        message = self.mailMocker.messageBuilder.create_message(
             attachments=[
                 _AttachmentDef(filename="f1.pdf"),
                 _AttachmentDef(
@@ -459,7 +531,7 @@ class TestMail(
         result = self.mail_account_handler._handle_message(message, rule)
 
         self.assertEqual(result, 1)
-        self.assert_queue_consumption_tasks_call_args(
+        self.mailMocker.assert_queue_consumption_tasks_call_args(
             [
                 [
                     {"override_filename": "f1.pdf"},
@@ -468,7 +540,7 @@ class TestMail(
         )
 
     def test_handle_disposition(self):
-        message = self.create_message(
+        message = self.mailMocker.messageBuilder.create_message(
             attachments=[
                 _AttachmentDef(
                     filename="f1.pdf",
@@ -487,7 +559,7 @@ class TestMail(
 
         result = self.mail_account_handler._handle_message(message, rule)
         self.assertEqual(result, 1)
-        self.assert_queue_consumption_tasks_call_args(
+        self.mailMocker.assert_queue_consumption_tasks_call_args(
             [
                 [
                     {"override_filename": "f2.pdf"},
@@ -496,7 +568,7 @@ class TestMail(
         )
 
     def test_handle_inline_files(self):
-        message = self.create_message(
+        message = self.mailMocker.messageBuilder.create_message(
             attachments=[
                 _AttachmentDef(
                     filename="f1.pdf",
@@ -516,7 +588,7 @@ class TestMail(
 
         result = self.mail_account_handler._handle_message(message, rule)
         self.assertEqual(result, 2)
-        self.assert_queue_consumption_tasks_call_args(
+        self.mailMocker.assert_queue_consumption_tasks_call_args(
             [
                 [
                     {"override_filename": "f1.pdf"},
@@ -536,7 +608,7 @@ class TestMail(
             - Mail action should not be performed for files excluded
             - Mail action should be performed for files included
         """
-        message = self.create_message(
+        message = self.mailMocker.messageBuilder.create_message(
             attachments=[
                 _AttachmentDef(filename="f1.pdf"),
                 _AttachmentDef(filename="f2.pdf"),
@@ -620,7 +692,7 @@ class TestMail(
 
         for test_case in tests:
             with self.subTest(msg=test_case.name):
-                self._queue_consumption_tasks_mock.reset_mock()
+                self.mailMocker._queue_consumption_tasks_mock.reset_mock()
                 account = MailAccount(name=str(uuid.uuid4()))
                 account.save()
                 rule = MailRule(
@@ -633,7 +705,7 @@ class TestMail(
                 rule.save()
 
                 self.mail_account_handler._handle_message(message, rule)
-                self.assert_queue_consumption_tasks_call_args(
+                self.mailMocker.assert_queue_consumption_tasks_call_args(
                     [
                         [{"override_filename": m} for m in test_case.expected_matches],
                     ],
@@ -648,7 +720,7 @@ class TestMail(
         THEN:
             - Mail action should not be performed
         """
-        message = self.create_message(
+        message = self.mailMocker.messageBuilder.create_message(
             attachments=[
                 _AttachmentDef(
                     filename="test.png",
@@ -656,7 +728,7 @@ class TestMail(
                 ),
             ],
         )
-        self.bogus_mailbox.messages.append(message)
+        self.mailMocker.bogus_mailbox.messages.append(message)
         account = MailAccount.objects.create(
             name="test",
             imap_server="",
@@ -674,12 +746,12 @@ class TestMail(
         )
         rule.save()
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 4)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 4)
 
         self.mail_account_handler.handle_mail_account(account)
-        self.apply_mail_actions()
+        self.mailMocker.apply_mail_actions()
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 1)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 1)
 
     def test_handle_mail_account_mark_read(self):
         account = MailAccount.objects.create(
@@ -695,14 +767,14 @@ class TestMail(
             action=MailRule.MailAction.MARK_READ,
         )
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 3)
-        self.assertEqual(len(self.bogus_mailbox.fetch("UNSEEN", False)), 2)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 3)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.fetch("UNSEEN", False)), 2)
 
         self.mail_account_handler.handle_mail_account(account)
-        self.apply_mail_actions()
+        self.mailMocker.apply_mail_actions()
 
-        self.assertEqual(len(self.bogus_mailbox.fetch("UNSEEN", False)), 0)
-        self.assertEqual(len(self.bogus_mailbox.messages), 3)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.fetch("UNSEEN", False)), 0)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 3)
 
     def test_handle_mail_account_delete(self):
         account = MailAccount.objects.create(
@@ -719,12 +791,12 @@ class TestMail(
             filter_subject="Invoice",
         )
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 3)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 3)
 
         self.mail_account_handler.handle_mail_account(account)
-        self.apply_mail_actions()
+        self.mailMocker.apply_mail_actions()
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 1)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 1)
 
     def test_handle_mail_account_delete_no_filters(self):
         account = MailAccount.objects.create(
@@ -741,12 +813,12 @@ class TestMail(
             maximum_age=0,
         )
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 3)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 3)
 
         self.mail_account_handler.handle_mail_account(account)
-        self.apply_mail_actions()
+        self.mailMocker.apply_mail_actions()
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 0)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 0)
 
     def test_handle_mail_account_flag(self):
         account = MailAccount.objects.create(
@@ -763,14 +835,20 @@ class TestMail(
             filter_subject="Invoice",
         )
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 3)
-        self.assertEqual(len(self.bogus_mailbox.fetch("UNFLAGGED", False)), 2)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 3)
+        self.assertEqual(
+            len(self.mailMocker.bogus_mailbox.fetch("UNFLAGGED", False)),
+            2,
+        )
 
         self.mail_account_handler.handle_mail_account(account)
-        self.apply_mail_actions()
+        self.mailMocker.apply_mail_actions()
 
-        self.assertEqual(len(self.bogus_mailbox.fetch("UNFLAGGED", False)), 1)
-        self.assertEqual(len(self.bogus_mailbox.messages), 3)
+        self.assertEqual(
+            len(self.mailMocker.bogus_mailbox.fetch("UNFLAGGED", False)),
+            1,
+        )
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 3)
 
     @pytest.mark.flaky(reruns=4)
     def test_handle_mail_account_move(self):
@@ -789,14 +867,14 @@ class TestMail(
             filter_subject="Claim",
         )
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 3)
-        self.assertEqual(len(self.bogus_mailbox.messages_spam), 0)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 3)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages_spam), 0)
 
         self.mail_account_handler.handle_mail_account(account)
-        self.apply_mail_actions()
+        self.mailMocker.apply_mail_actions()
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 2)
-        self.assertEqual(len(self.bogus_mailbox.messages_spam), 1)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 2)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages_spam), 1)
 
     def test_handle_mail_account_move_no_filters(self):
         account = MailAccount.objects.create(
@@ -814,14 +892,14 @@ class TestMail(
             maximum_age=0,
         )
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 3)
-        self.assertEqual(len(self.bogus_mailbox.messages_spam), 0)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 3)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages_spam), 0)
 
         self.mail_account_handler.handle_mail_account(account)
-        self.apply_mail_actions()
+        self.mailMocker.apply_mail_actions()
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 0)
-        self.assertEqual(len(self.bogus_mailbox.messages_spam), 3)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 0)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages_spam), 3)
 
     def test_handle_mail_account_tag(self):
         account = MailAccount.objects.create(
@@ -838,18 +916,24 @@ class TestMail(
             action_parameter="processed",
         )
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 3)
-        self.assertEqual(len(self.bogus_mailbox.fetch("UNKEYWORD processed", False)), 2)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 3)
+        self.assertEqual(
+            len(self.mailMocker.bogus_mailbox.fetch("UNKEYWORD processed", False)),
+            2,
+        )
 
         self.mail_account_handler.handle_mail_account(account)
-        self.apply_mail_actions()
+        self.mailMocker.apply_mail_actions()
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 3)
-        self.assertEqual(len(self.bogus_mailbox.fetch("UNKEYWORD processed", False)), 0)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 3)
+        self.assertEqual(
+            len(self.mailMocker.bogus_mailbox.fetch("UNKEYWORD processed", False)),
+            0,
+        )
 
     def test_handle_mail_account_tag_gmail(self):
-        self.bogus_mailbox._host = "imap.gmail.com"
-        self.bogus_mailbox.client.capabilities = ["X-GM-EXT-1"]
+        self.mailMocker.bogus_mailbox._host = "imap.gmail.com"
+        self.mailMocker.bogus_mailbox.client.capabilities = ["X-GM-EXT-1"]
 
         account = MailAccount.objects.create(
             name="test",
@@ -865,15 +949,15 @@ class TestMail(
             action_parameter="processed",
         )
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 3)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 3)
         criteria = NOT(gmail_label="processed")
-        self.assertEqual(len(self.bogus_mailbox.fetch(criteria, False)), 2)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.fetch(criteria, False)), 2)
 
         self.mail_account_handler.handle_mail_account(account)
-        self.apply_mail_actions()
+        self.mailMocker.apply_mail_actions()
 
-        self.assertEqual(len(self.bogus_mailbox.fetch(criteria, False)), 0)
-        self.assertEqual(len(self.bogus_mailbox.messages), 3)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.fetch(criteria, False)), 0)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 3)
 
     def test_tag_mail_action_applemail_wrong_input(self):
         self.assertRaises(
@@ -900,14 +984,20 @@ class TestMail(
             action_parameter="apple:green",
         )
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 3)
-        self.assertEqual(len(self.bogus_mailbox.fetch("UNFLAGGED", False)), 2)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 3)
+        self.assertEqual(
+            len(self.mailMocker.bogus_mailbox.fetch("UNFLAGGED", False)),
+            2,
+        )
 
         self.mail_account_handler.handle_mail_account(account)
-        self.apply_mail_actions()
+        self.mailMocker.apply_mail_actions()
 
-        self.assertEqual(len(self.bogus_mailbox.fetch("UNFLAGGED", False)), 0)
-        self.assertEqual(len(self.bogus_mailbox.messages), 3)
+        self.assertEqual(
+            len(self.mailMocker.bogus_mailbox.fetch("UNFLAGGED", False)),
+            0,
+        )
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 3)
 
     def test_error_login(self):
         """
@@ -955,10 +1045,10 @@ class TestMail(
         )
 
         tasks.process_mail_accounts()
-        self.apply_mail_actions()
+        self.mailMocker.apply_mail_actions()
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 2)
-        self.assertEqual(len(self.bogus_mailbox.messages_spam), 1)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 2)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages_spam), 1)
 
     def test_error_skip_rule(self):
         account = MailAccount.objects.create(
@@ -986,10 +1076,10 @@ class TestMail(
         )
 
         self.mail_account_handler.handle_mail_account(account)
-        self.apply_mail_actions()
+        self.mailMocker.apply_mail_actions()
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 2)
-        self.assertEqual(len(self.bogus_mailbox.messages_spam), 1)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 2)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages_spam), 1)
 
     def test_error_folder_set(self):
         """
@@ -1015,14 +1105,14 @@ class TestMail(
             folder="uuuhhhh",  # Invalid folder name
         )
 
-        self.bogus_mailbox.folder.list = mock.Mock(
+        self.mailMocker.bogus_mailbox.folder.list = mock.Mock(
             return_value=[FolderInfo("SomeFoldername", "|", ())],
         )
 
         self.mail_account_handler.handle_mail_account(account)
 
-        self.bogus_mailbox.folder.list.assert_called_once()
-        self._queue_consumption_tasks_mock.assert_not_called()
+        self.mailMocker.bogus_mailbox.folder.list.assert_called_once()
+        self.mailMocker._queue_consumption_tasks_mock.assert_not_called()
 
     def test_error_folder_set_error_listing(self):
         """
@@ -1048,14 +1138,14 @@ class TestMail(
             folder="uuuhhhh",  # Invalid folder name
         )
 
-        self.bogus_mailbox.folder.list = mock.Mock(
+        self.mailMocker.bogus_mailbox.folder.list = mock.Mock(
             side_effect=MailboxFolderSelectError(None, "uhm"),
         )
 
         self.mail_account_handler.handle_mail_account(account)
 
-        self.bogus_mailbox.folder.list.assert_called_once()
-        self._queue_consumption_tasks_mock.assert_not_called()
+        self.mailMocker.bogus_mailbox.folder.list.assert_called_once()
+        self.mailMocker._queue_consumption_tasks_mock.assert_not_called()
 
     @mock.patch("paperless_mail.mail.MailAccountHandler._get_correspondent")
     def test_error_skip_mail(self, m):
@@ -1081,14 +1171,17 @@ class TestMail(
         )
 
         self.mail_account_handler.handle_mail_account(account)
-        self.apply_mail_actions()
+        self.mailMocker.apply_mail_actions()
 
         # test that we still consume mail even if some mails throw errors.
-        self.assertEqual(self._queue_consumption_tasks_mock.call_count, 2)
+        self.assertEqual(self.mailMocker._queue_consumption_tasks_mock.call_count, 2)
 
         # faulty mail still in inbox, untouched
-        self.assertEqual(len(self.bogus_mailbox.messages), 1)
-        self.assertEqual(self.bogus_mailbox.messages[0].from_, "amazon@amazon.de")
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 1)
+        self.assertEqual(
+            self.mailMocker.bogus_mailbox.messages[0].from_,
+            "amazon@amazon.de",
+        )
 
     def test_error_create_correspondent(self):
         account = MailAccount.objects.create(
@@ -1108,10 +1201,10 @@ class TestMail(
 
         self.mail_account_handler.handle_mail_account(account)
 
-        self._queue_consumption_tasks_mock.assert_called_once()
+        self.mailMocker._queue_consumption_tasks_mock.assert_called_once()
 
         c = Correspondent.objects.get(name="amazon@amazon.de")
-        self.assert_queue_consumption_tasks_call_args(
+        self.mailMocker.assert_queue_consumption_tasks_call_args(
             [
                 [
                     {"override_correspondent_id": c.id},
@@ -1119,15 +1212,18 @@ class TestMail(
             ],
         )
 
-        self._queue_consumption_tasks_mock.reset_mock()
-        self.reset_bogus_mailbox()
+        self.mailMocker._queue_consumption_tasks_mock.reset_mock()
+        reset_bogus_mailbox(
+            self.mailMocker.bogus_mailbox,
+            self.mailMocker.messageBuilder,
+        )
 
         with mock.patch("paperless_mail.mail.Correspondent.objects.get_or_create") as m:
             m.side_effect = DatabaseError()
 
             self.mail_account_handler.handle_mail_account(account)
 
-        self.assert_queue_consumption_tasks_call_args(
+        self.mailMocker.assert_queue_consumption_tasks_call_args(
             [
                 [
                     {"override_correspondent_id": None},
@@ -1165,21 +1261,24 @@ class TestMail(
                     filter_from=f_from,
                     filter_to=f_to,
                 )
-                self.reset_bogus_mailbox()
-                self._queue_consumption_tasks_mock.reset_mock()
+                reset_bogus_mailbox(
+                    self.mailMocker.bogus_mailbox,
+                    self.mailMocker.messageBuilder,
+                )
+                self.mailMocker._queue_consumption_tasks_mock.reset_mock()
 
-                self._queue_consumption_tasks_mock.assert_not_called()
-                self.assertEqual(len(self.bogus_mailbox.messages), 3)
+                self.mailMocker._queue_consumption_tasks_mock.assert_not_called()
+                self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 3)
 
                 self.mail_account_handler.handle_mail_account(account)
-                self.apply_mail_actions()
+                self.mailMocker.apply_mail_actions()
 
                 self.assertEqual(
-                    len(self.bogus_mailbox.messages),
+                    len(self.mailMocker.bogus_mailbox.messages),
                     3 - expected_mail_count,
                 )
                 self.assertEqual(
-                    self._queue_consumption_tasks_mock.call_count,
+                    self.mailMocker._queue_consumption_tasks_mock.call_count,
                     expected_mail_count,
                 )
 
@@ -1206,16 +1305,16 @@ class TestMail(
             action=MailRule.MailAction.MARK_READ,
         )
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 3)
-        self._queue_consumption_tasks_mock.assert_not_called()
-        self.assertEqual(len(self.bogus_mailbox.fetch("UNSEEN", False)), 2)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 3)
+        self.mailMocker._queue_consumption_tasks_mock.assert_not_called()
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.fetch("UNSEEN", False)), 2)
 
         self.mail_account_handler.handle_mail_account(account)
-        self.apply_mail_actions()
+        self.mailMocker.apply_mail_actions()
 
-        self.assertEqual(self._queue_consumption_tasks_mock.call_count, 2)
-        self.assertEqual(len(self.bogus_mailbox.fetch("UNSEEN", False)), 0)
-        self.assertEqual(len(self.bogus_mailbox.messages), 3)
+        self.assertEqual(self.mailMocker._queue_consumption_tasks_mock.call_count, 2)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.fetch("UNSEEN", False)), 0)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 3)
 
     def test_auth_plain_fallback_fails_still(self):
         """
@@ -1272,75 +1371,16 @@ class TestMail(
             action=MailRule.MailAction.MARK_READ,
         )
 
-        self.assertEqual(len(self.bogus_mailbox.messages), 3)
-        self.assertEqual(self._queue_consumption_tasks_mock.call_count, 0)
-        self.assertEqual(len(self.bogus_mailbox.fetch("UNSEEN", False)), 2)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 3)
+        self.assertEqual(self.mailMocker._queue_consumption_tasks_mock.call_count, 0)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.fetch("UNSEEN", False)), 2)
 
         self.mail_account_handler.handle_mail_account(account)
-        self.apply_mail_actions()
-
-        self.assertEqual(self._queue_consumption_tasks_mock.call_count, 2)
-        self.assertEqual(len(self.bogus_mailbox.fetch("UNSEEN", False)), 0)
-        self.assertEqual(len(self.bogus_mailbox.messages), 3)
-
-    def assert_queue_consumption_tasks_call_args(
-        self,
-        expected_call_args: list[list[dict[str, str]]],
-    ):
-        """
-        Verifies that queue_consumption_tasks has been called with the expected arguments.
-
-        expected_call_args is the following format:
-
-        * List of calls to queue_consumption_tasks, called once per mail, where each element is:
-        * List of signatures for the consume_file task, where each element is:
-        * dictionary containing arguments that need to be present in the consume_file signature.
-
-        """
-
-        # assert number of calls to queue_consumption_tasks match
-        self.assertEqual(
-            len(self._queue_consumption_tasks_mock.call_args_list),
-            len(expected_call_args),
-        )
-
-        for (mock_args, mock_kwargs), expected_signatures in zip(
-            self._queue_consumption_tasks_mock.call_args_list,
-            expected_call_args,
-        ):
-            consume_tasks = mock_kwargs["consume_tasks"]
-
-            # assert number of consume_file tasks match
-            self.assertEqual(len(consume_tasks), len(expected_signatures))
-
-            for consume_task, expected_signature in zip(
-                consume_tasks,
-                expected_signatures,
-            ):
-                input_doc, overrides = consume_task.args
-
-                # assert the file exists
-                self.assertIsFile(input_doc.original_file)
-
-                # assert all expected arguments are present in the signature
-                for key, value in expected_signature.items():
-                    if key == "override_correspondent_id":
-                        self.assertEqual(overrides.correspondent_id, value)
-                    elif key == "override_filename":
-                        self.assertEqual(overrides.filename, value)
-                    elif key == "override_title":
-                        self.assertEqual(overrides.title, value)
-                    else:
-                        self.fail("No match for expected arg")
+        self.mailMocker.apply_mail_actions()
 
-    def apply_mail_actions(self):
-        """
-        Applies pending actions to mails by inspecting calls to the queue_consumption_tasks method.
-        """
-        for args, kwargs in self._queue_consumption_tasks_mock.call_args_list:
-            message = kwargs["message"]
-            rule = kwargs["rule"]
-            apply_mail_action([], rule.pk, message.uid, message.subject, message.date)
+        self.assertEqual(self.mailMocker._queue_consumption_tasks_mock.call_count, 2)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.fetch("UNSEEN", False)), 0)
+        self.assertEqual(len(self.mailMocker.bogus_mailbox.messages), 3)
 
 
 class TestManagementCommand(TestCase):

diff --git a/src/paperless_mail/tests/test_preprocessor.py b/src/paperless_mail/tests/test_preprocessor.py
new file mode 100644 (file)
index 0000000..90df77b
--- /dev/null
+++ b/src/paperless_mail/tests/test_preprocessor.py
@@ -0,0 +1,228 @@
+import email
+import email.contentmanager
+import tempfile
+from email.message import Message
+from email.mime.application import MIMEApplication
+from email.mime.multipart import MIMEMultipart
+from unittest import mock
+
+import gnupg
+from django.test import override_settings
+from imap_tools import MailMessage
+
+from paperless_mail.mail import MailAccountHandler
+from paperless_mail.models import MailAccount
+from paperless_mail.models import MailRule
+from paperless_mail.preprocessor import MailMessageDecryptor
+from paperless_mail.tests.test_mail import TestMail
+from paperless_mail.tests.test_mail import _AttachmentDef
+
+
+class MessageEncryptor:
+    def __init__(self):
+        self.gpg_home = tempfile.mkdtemp()
+        self.gpg = gnupg.GPG(gnupghome=self.gpg_home)
+        self._testUser = "testuser@example.com"
+        # Generate a new key
+        input_data = self.gpg.gen_key_input(
+            name_email=self._testUser,
+            passphrase=None,
+            key_type="RSA",
+            key_length=2048,
+            expire_date=0,
+            no_protection=True,
+        )
+        self.gpg.gen_key(input_data)
+
+    @staticmethod
+    def get_email_body_without_headers(email_message: Message) -> bytes:
+        """
+        Filters some relevant headers from an EmailMessage and returns just the body.
+        """
+        message_copy = email.message_from_bytes(email_message.as_bytes())
+
+        message_copy._headers = [
+            header
+            for header in message_copy._headers
+            if header[0].lower() not in ("from", "to", "subject")
+        ]
+        return message_copy.as_bytes()
+
+    def encrypt(self, message):
+        original_email: email.message.Message = message.obj
+        encrypted_data = self.gpg.encrypt(
+            self.get_email_body_without_headers(original_email),
+            self._testUser,
+            armor=True,
+        )
+        if not encrypted_data.ok:
+            raise Exception(f"Encryption failed: {encrypted_data.stderr}")
+        encrypted_email_content = encrypted_data.data
+
+        new_email = MIMEMultipart("encrypted", protocol="application/pgp-encrypted")
+        new_email["From"] = original_email["From"]
+        new_email["To"] = original_email["To"]
+        new_email["Subject"] = original_email["Subject"]
+
+        # Add the control part
+        control_part = MIMEApplication(_data=b"", _subtype="pgp-encrypted")
+        control_part.set_payload("Version: 1")
+        new_email.attach(control_part)
+
+        # Add the encrypted data part
+        encrypted_part = MIMEApplication(_data=b"", _subtype="octet-stream")
+        encrypted_part.set_payload(encrypted_email_content.decode("ascii"))
+        encrypted_part.add_header(
+            "Content-Disposition",
+            'attachment; filename="encrypted.asc"',
+        )
+        new_email.attach(encrypted_part)
+
+        encrypted_message: MailMessage = MailMessage(
+            [(f"UID {message.uid}".encode(), new_email.as_bytes())],
+        )
+        return encrypted_message
+
+
+class TestMailMessageGpgDecryptor(TestMail):
+    def setUp(self):
+        self.messageEncryptor = MessageEncryptor()
+        with override_settings(
+            EMAIL_GNUPG_HOME=self.messageEncryptor.gpg_home,
+            EMAIL_ENABLE_GPG_DECRYPTOR=True,
+        ):
+            super().setUp()
+
+    def test_preprocessor_is_able_to_run(self):
+        with override_settings(
+            EMAIL_GNUPG_HOME=self.messageEncryptor.gpg_home,
+            EMAIL_ENABLE_GPG_DECRYPTOR=True,
+        ):
+            self.assertTrue(MailMessageDecryptor.able_to_run())
+
+    def test_preprocessor_is_able_to_run2(self):
+        with override_settings(
+            EMAIL_GNUPG_HOME=None,
+            EMAIL_ENABLE_GPG_DECRYPTOR=True,
+        ):
+            self.assertTrue(MailMessageDecryptor.able_to_run())
+
+    def test_is_not_able_to_run_disabled(self):
+        with override_settings(
+            EMAIL_ENABLE_GPG_DECRYPTOR=False,
+        ):
+            self.assertFalse(MailMessageDecryptor.able_to_run())
+
+    def test_is_not_able_to_run_bogus_path(self):
+        with override_settings(
+            EMAIL_ENABLE_GPG_DECRYPTOR=True,
+            EMAIL_GNUPG_HOME="_)@# notapath &%#$",
+        ):
+            self.assertFalse(MailMessageDecryptor.able_to_run())
+
+    def test_fails_at_initialization(self):
+        with (
+            mock.patch("gnupg.GPG.__init__") as mock_run,
+            override_settings(
+                EMAIL_ENABLE_GPG_DECRYPTOR=True,
+            ),
+        ):
+
+            def side_effect(*args, **kwargs):
+                raise OSError("Cannot find 'gpg' binary")
+
+            mock_run.side_effect = side_effect
+
+            handler = MailAccountHandler()
+            self.assertEqual(len(handler._message_preprocessors), 0)
+
+    def test_decrypt_fails(self):
+        encrypted_message, _ = self.create_encrypted_unencrypted_message_pair()
+        empty_gpg_home = tempfile.mkdtemp()
+        with override_settings(
+            EMAIL_ENABLE_GPG_DECRYPTOR=True,
+            EMAIL_GNUPG_HOME=empty_gpg_home,
+        ):
+            message_decryptor = MailMessageDecryptor()
+            self.assertRaises(Exception, message_decryptor.run, encrypted_message)
+
+    def test_decrypt_encrypted_mail(self):
+        """
+        Creates a mail with attachments. Then encrypts it with a new key.
+        Verifies that this encrypted message can be decrypted with attachments intact.
+        """
+        encrypted_message, message = self.create_encrypted_unencrypted_message_pair()
+        headers = message.headers
+        text = message.text
+
+        self.assertEqual(len(encrypted_message.attachments), 1)
+        self.assertEqual(encrypted_message.attachments[0].filename, "encrypted.asc")
+        self.assertEqual(encrypted_message.text, "")
+
+        with override_settings(
+            EMAIL_ENABLE_GPG_DECRYPTOR=True,
+            EMAIL_GNUPG_HOME=self.messageEncryptor.gpg_home,
+        ):
+            message_decryptor = MailMessageDecryptor()
+            self.assertTrue(message_decryptor.able_to_run())
+            decrypted_message = message_decryptor.run(encrypted_message)
+
+        self.assertEqual(len(decrypted_message.attachments), 2)
+        self.assertEqual(decrypted_message.attachments[0].filename, "f1.pdf")
+        self.assertEqual(decrypted_message.attachments[1].filename, "f2.pdf")
+        self.assertEqual(decrypted_message.headers, headers)
+        self.assertEqual(decrypted_message.text, text)
+        self.assertEqual(decrypted_message.uid, message.uid)
+
+    def create_encrypted_unencrypted_message_pair(self):
+        message = self.mailMocker.messageBuilder.create_message(
+            body="Test message with 2 attachments",
+            attachments=[
+                _AttachmentDef(
+                    filename="f1.pdf",
+                    disposition="inline",
+                ),
+                _AttachmentDef(filename="f2.pdf"),
+            ],
+        )
+        encrypted_message = self.messageEncryptor.encrypt(message)
+        return encrypted_message, message
+
+    def test_handle_encrypted_message(self):
+        message = self.mailMocker.messageBuilder.create_message(
+            subject="the message title",
+            from_="Myself",
+            attachments=2,
+            body="Test mail",
+        )
+
+        encrypted_message = self.messageEncryptor.encrypt(message)
+
+        account = MailAccount.objects.create()
+        rule = MailRule(
+            assign_title_from=MailRule.TitleSource.FROM_FILENAME,
+            consumption_scope=MailRule.ConsumptionScope.EVERYTHING,
+            account=account,
+        )
+        rule.save()
+
+        result = self.mail_account_handler._handle_message(encrypted_message, rule)
+
+        self.assertEqual(result, 3)
+
+        self.mailMocker._queue_consumption_tasks_mock.assert_called()
+
+        self.mailMocker.assert_queue_consumption_tasks_call_args(
+            [
+                [
+                    {
+                        "override_title": message.subject,
+                        "override_filename": f"{message.subject}.eml",
+                    },
+                ],
+                [
+                    {"override_title": "file_0", "override_filename": "file_0.pdf"},
+                    {"override_title": "file_1", "override_filename": "file_1.pdf"},
+                ],
+            ],
+        )