Update to 4.37.0. From the changelog:

- handle IMAP servers which include "/" in message IDs better, so
  those messages aren't always thought to be new. Thanks: Bradley
  Rintoul.

- record (IMAP) mailbox retrieved from in X-getmail-retrieved-from-mailbox:
  header field, and make it available as %(mailbox) substitution
  in MDA_external arguments. Thanks: Les Barstow.

- add delete_bigger_than option to allow removal of large messages
  after retrieval, even if not deleting messages otherwise. Thanks:
  Jan Vereecke.

(schmonz)