Ask HN: What do you look for in a mail-client application?

Over the past few months I've built a console-based mail-client. Although inspired by mutt it is pretty different due to the user-interface, and the awesome built-in scripting which is provided via Lua.

The existing client is available from github, and is documented extensively on the website : http://lumail.org/

Recently I've been pondering splitting things up into a client/server model. Having a persistent deamon process, to which the GUI would talk.

This would allow both a console-based client and a GUI client to be constructed. Before I go down this road I wonder if there is room for another client, and if so what features people would like in local-clients.

I expect the obvious are .. obvious: IMAP, POP3, GPG, searching, etc, etc. But I wonder what I'm missing.

One thing that I've liked about the current client, which I think is almost unique, is the notion of opening multiple folders at once. But one thing I'm sold on is that the scripting support must remain, it is just too useful!