I've got a bunch of duplicate messages in my IMAP server's Maildir. What's the best way to remove them?

Some relevant points:

  • Shared Message-ID is usually a good enough definition of duplicate. A tiny script that removes all but one of the duplicate messages would work.
  • Sometimes it's necessary to find duplicates based on shared message bodies. What's a reasonable definition of shared here? Bitwise equivalent? What about weird differences in line wrapping, escaping, character encoding?
  • Sometimes there's some meaningful difference between 'duplicate' messages. What's the best way to review the differences in sets of 'duplicate' messages? Diffs?

I've made some significant improvements to Kevin's script mentioned above, and he was kind enough to accept my pull requests. Eventually we split this off into a dedicated project which you can find here:



for generic files in linux, I use fdupes utils to remove duplicate files. I found it also works for Maildir messages.

  • 1
    fdupes seems to work for exact duplicates only, while the OP is (implicitly) asking about more complex patterns of duplication. A message delivered twice because of .forward or whatever will have slightly different headers, so while the message itself is a duplicate, the two files containing the two copies may not be. – tripleee Feb 6 '17 at 6:55

Gnome's Evolution [a graphical mail user agent] has a built-in feature to remove duplicate mail. As explained on this help page, it boils down to:

  1. Select the suspect messages (or just all messages)
  2. Go to menu Messages, the choose Remove Duplicate Messages.


P.S. Evolution can access your messages locally (MailDir, MH, Mbox) or over IMAP.


Best I've found today is Kevin Deldycke's maildir-deduplicate.

  • It ignores the X-MIMETrack header by default and compares headers using the SHA224 digest.
  • It automatically deletes duplicates without asking for confirmation; however there is a dry-run mode which allows previewing which duplicates will be deleted.

I bet someone could make something fancy from Rick Sanders' delIMAPdups.pl, part of his IMAP Tools.

  • maildir-deduplicate moved to a new location so I updated the link. However your information is now out of date. – Adam Spiers Feb 3 '14 at 12:32
  • I've updated this so that there is no longer misleading outdated info. – Adam Spiers Jun 13 '19 at 11:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.