We deployed new code was today that includes a fix to support the popular free Email service GMX. There have been quite a few users attempting to use GMX with push email free trial accounts and it wasn't until I tried GMX myself that we discovered there was an incompatibility with their IMAP service. Fortunately the problem was easy to fix.
In testing with GMX we've noticed that message read/un-read changes are pushed (unlike GMail) but message delete events are sometimes delayed by up to a minute.
Correct push email configuration on our web site for GMX looks like this: