lib-index: Update mail_index_mail_flags comments and add MAIL_INDEX_MAIL_FLAG_UNUSED

diff --git a/src/lib-index/mail-index.h b/src/lib-index/mail-index.h
index bcc312b7395dd669433e981ff1137d76c8802ae0..577287e9fc803e06572dd6e698f40ec8df0baba9 100644 (file)
--- a/src/lib-index/mail-index.h
+++ b/src/lib-index/mail-index.h
@@ -62,13 +62,18 @@ enum mail_index_header_flag {
 };
 
 enum mail_index_mail_flags {
+       /* This flag used to contain MAIL_RECENT flag, but is always zero
+          with the current index file format. */
+       MAIL_INDEX_MAIL_FLAG_UNUSED             = 0x20,
        /* For private use by backend. Replacing flags doesn't change this. */
        MAIL_INDEX_MAIL_FLAG_BACKEND            = 0x40,
        /* Message flags haven't been written to backend. If
           MAIL_INDEX_OPEN_FLAG_NO_DIRTY is set, this is treated as a
           backend-specific flag with no special internal handling. */
        MAIL_INDEX_MAIL_FLAG_DIRTY              = 0x80,
-       /* Force updating this message's modseq via a flag update record */
+
+       /* Force updating this message's modseq via a flag update record.
+          Note that this flag isn't saved to disk. */
        MAIL_INDEX_MAIL_FLAG_UPDATE_MODSEQ      = 0x100
 };