Our IMAP server (Cyrus) has been upgraded to a new version, which includes some additional features we commissioned:

  1. Fuzzy folder matching in delivery. When you use the + or sub-domain
    folders are now matched, and if not found, a fuzzy match is done. In
    the fuzzy match scenario, folders are compared in a case insensitive
    way, and with the chars "-", "_" and " " (space) all treated as the
    same. So if you have a folder "Mailing Lists.My List", then sending
    to username+mailing-lists.my_list@domain.tld will get filed into
    that folder
  2. File to parent if sub-folder missing. If in the matching scenario,
    the sub-folder still isn't found, but a parent folder is, that
    folder is delivered to instead. So if you sent to
    username+mailing-lists.blahblahblah@domain.tld, the email would go
    into the "Mailing Lists" folder, rather than the inbox
  3. POP to sub-folders. If you login via POP with the username
    "username+foldername", then you'll be able to POP messages from that
    subfolder, not just inbox. This currently doesn't work for folders
    with spaces in the name unfortunately.
  4. Faster message moving/deleting. Internally cyrus now uses a "delayed
    expunge" mode. In small folders, this won't make much difference,
    but in large folders, it makes moving or deleting messages quite a
    bit faster.

For more information, see this discussion on the forum.