FastMail has a special proxy system whereby you can access each service (POP, IMAP, SMTP, etc) through any port number by using special server names.
Note: You should only use these proxy servers if you can’t use the standard server names and ports. You should only use them if you know what you’re doing. For a list of standard server names and ports, see our help page - http://www.fastmail.fm/help/remote_email_access_server_names_and_ports.html
Originally, the server names for the proxy services were of the form imap.proxy.fastmail.fm, imaps.proxy.fastmail.fm, pop.proxy.fastmail.fm, etc.
To make these services consistent with our main server names (eg mail.messagingengine.com, chat.messagingengine.com, etc) and to make them work with SSL, we changed to using imap.proxy.messagingengine.com, imaps.proxy.messagingengine.com, etc.
Unfortunately, it appears that we got this wrong because wildcard SSL certificates (eg. like are *.messagingengine.com one) only match a single level deep domain. Because of that, we’re changing our official proxy server names again to the following:
If you’re using the proxy servers, please update your software to use the new appropriate name.