I put even more work into Liam this weekend, and added and improved several things. For example, it is now possible to save attachments or even complete mails to your local file system. I improved handling of MIME types with attachments, including choosing the best encoding for the mail body and each attachment. And even such small things as defining a signoff string, a signature file or your preferred editor have been implemented. The performance issues that I previously experienced with the file browser are no more, I was able to identify the problem and fix it.
And so far, I only have a few more big TODOs on my list, like moving mails to other folders, a search function, a notification when new mails arrive while the mailbox is open and a scripting interface to make Liam scriptable and more customizable. Support for other protocols and storage formats is also missing, but e.g. support for Maildir(++) and MBOX should be pretty easy to implement. What I also have in my mind is a (hear! hear!) disconnected mode that should make it possible to read mails that have been downloaded previously, but that lies a bit farther in the future.
That's my status report so far, feedback is as usual welcome.