A Python script for creating full backups of IMAP mailboxes

This was first published around 2007 (probably earlier) on my personal site, and it was originally developed to work around the then rather limited (ok, inconsistent) Mac OS X Mail.app functionality and allow me to back up my old mailboxes in a fully standard mbox format (well, at least as much as mbox can be considered a standard...).

Somewhat to my surprise it was considered useful by quite a few people throughout the years, and contributions started coming in. Given that there seems to be renewed interest in this as a systems administration tool, I'm posting the source code here and re-licensing it under the MIT license.

• ZERO dependencies.
• Copies every single message from every single folder (or a subset of folders) in your IMAP server to your disk.
• Does incremental copying (i.e., tries very hard to not copy messages twice).
• Tries to do everything as safely as possible (only performs read operations on IMAP).
• Generates mbox formatted files that can be imported into Mail.app (just choose "Other" on the import dialog).
• Optionally compresses the result files on the fly (and can append to them). Only available in Python 2.x
• Is completely and utterly free (distributed under the MIT license).

Python 2.x : imapbackup.py should work on Python 2.5 or any other 2.x version without any extra dependencies whatsoever. Python 3.x : imapbackup38.py requires python 3.8 and above.

I am accepting pull requests, but bear in mind that one of the original goals of this script was to run on older Python versions, so as to save sysadmins stuck in the Dark Ages the trouble of installing a newer Python (much to my own amazement, this was originally written in Python 2.3).

I would be delighted to bring it fully up to date with Python 2.7.x/3.x, etc., and have considered adding multi-threading/multiprocessing to speed it up, but time is short enough as it is. If you feel up to the task just send me a pull request with a "new" main script with the target Python version as part of its name - something like imapbackup27.py, imapbackup39.py, etc.

For tradition's sake, here goes:

IN NO EVENT WILL I BE LIABLE FOR ANY DAMAGES WHATSOEVER (INCLUDING, WITHOUT LIMITATION, THOSE RESULTING FROM LOST PROFITS, LOST DATA, LOST REVENUE OR BUSINESS INTERRUPTION) ARISING OUT OF THE USE, INABILITY TO USE, OR THE RESULTS OF USE OF, THIS PROGRAM. WITHOUT LIMITING THE FOREGOING, I SHALL NOT BE LIABLE FOR ANY SPECIAL, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL DAMAGES THAT MAY RESULT FROM THE USE OF THIS SCRIPT OR ANY PORTION THEREOF WHETHER ARISING UNDER CONTRACT, NEGLIGENCE, TORT OR ANY OTHER LAW OR CAUSE OF ACTION. I WILL ALSO PROVIDE NO SUPPORT WHATSOEVER, OTHER THAN ACCEPTING FIXES AND UPDATING THE SCRIPT AS IS DEEMED NECESSARY.