Thunderbird is my favorite email client. It works perfect with a IMAP Server. The only inconvenience is it do not have a build-in solution to sync message filters between computers, nor does it has an actively maintained filter import/export plugin. So far, the best solutions I find is to use Dropbox to sync the message filter rules.
The message filter rules is stored in
msgFilterRules.dat file located in each account directory. It can flawlessly be copied from one computer to another. Also, it can be safely synced between computer by Dropbox. You can use a soft link point to a
msgFilterRules.data file in my Dropbox, so that the filters can synced seamlessly.