[Fetchmail-announce] The 6.6.6 critical bug fix release of fetchmail is available (fixes IMAP confusion on unexpected EXPUNGE)

[Matthias A. <mat...@gm...>]

The 6.6.6 critical bug fix release of fetchmail is now available at the 
usual locations, including <https://downloads.sourceforge.net/project/fetchmail/branch_6.6/>.

People who cannot update but use IMAP should set "keep" or use "--keep" 
on the command line immediately to avoid accidentally deleting the wrong 
message in case your upstream IMAP server sees multiple clients on the 
same mailbox OR expunge automatically when a \Deleted flag is STOREd on 
a message.  A proper fix for this would be too large and/or risky and/or
introduce breaking changes, so is unsuitable for 6.6.x.

The source archive is available at:
<https://downloads.sourceforge.net/project/fetchmail/branch_6.6/fetchmail-6.6.6.tar.xz/download>

The detached GnuPG signature is available at:
<https://downloads.sourceforge.net/project/fetchmail/branch_6.6/fetchmail-6.6.6.tar.xz.asc/download>

The SHA256 hashes for the tarballs are:
SHA2-256(fetchmail-6.6.6.tar.xz)= da99f8c573c4d9e63f493c7e24447126aea25b53b4c076ec79266874e29b1975


Here are the release notes:
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fetchmail-6.6.6 (released 2026-06-24, 32443 LoC):

## CRITICAL BUGFIX FOR IMAP:
* The IMAP client, which has always used message indexes for the selected
  mailbox, did not abort when receiving an EXPUNGE response - which changes
  message numbers inside the mailbox.  Unlike UIDs, the message numbers are
  not stable and fetchmail does not have internal interfaces to track which
  messages are deleted, and adding those to a 6.6.X release would be too
  risky, and switching to UID is also too big a change, so we have no
  choice but to abort the session when seeing an EXPUNGE response without
  our own EXPUNGE request, to avoid marking the wrong message as seen/deleted
  or skip the wrong one, or assume the wrong message size.
  Earl Chew reported this versus Yahoo Mail via Gitlab Work Item #91, which
  automatically expunges messages that are marked with the \Deleted flag.

  This has one new message for which we do not have translations yet,
  it is urgent to get the fix in the field.

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