[Fixup]

In addition to gmail, xImapPusher also works perfectly with fastmail. Make sure you use this setting for fastmail:

mail.messagingengine.com:993

I tested it with a free account, no problem at all, faster than gmail. Both the single version and the multiple version work fine. It's really cool to push both gmail and fastmail at the same time!

Should work with more imap servers, as long as you find out the correct domain name. For example, imap.fastmail.fm won't work with xImapPusher, even though it does work for Outlook. If you ping, you can see the IP addresses are different for imap.fastmail.fm and mail.messagingengine.com.