A few months back, we blogged about a new compression proxy we had developed that helped improve IMAP performance. If you’re using an email client to access FastMail via IMAP, then the compression proxy can significantly speed up access to your account, especially if you have large folders with lots of messages (I use it, and see > 80% bandwidth savings on average)
However if you’re a bleeding edge email user, and are trying out the Thunderbird beta releases, then definitely download the latest Thunderbird 3 beta 3 as it now includes native support for the COMPRESS extension. This means you don’t need to use the proxy at all, you can just setup Thunderbird to access our server as normal (server name = mail.messagingengine.com) and it’ll automatically use the compressed protocol.
We don’t recommend using Thunderbird 3 yet if you’re a regular email user. It’s still definitely a beta, and has many known bugs. But if you like trying out new software and are aware of the potential caveats, then definitely give it a go!