Log Message:
Update to 4.52.0. From the changelog:

- add `ignore_header_shrinkage` parameter to Filter_external for users
  who know it is normal for their particular filter to result in a
  smaller message header than the source message, for example when the
  filter encapsulates the original message in a simpler wrapper message.
  Thanks: "RW", Tristan Miller, Francesco Ariis.
- EXPERIMENTAL: when deleting a message from an IMAP mailbox, set the
  \Seen flag in addition to the the \Deleted flag. This apparently
  prevents the ever-innovatively-broken MSExchange from sending a
  spurious incorrect disposition-notification message to the sender of
  the message. I do not know if this will cause problems with other
  broken IMAP server implementations; please send a report to the getmail-
  user's mailing list if you see odd behaviour with this change. Thanks:
  John Hein.
- enable socket timeouts for IMAP SSL classes by default. They were
  disabled in the code because they were incompatible with SSL in older
  versions of Python. If you see problems with Python 2.6 or 2.7 now,
  please let me know.