Hi,
First of all, can I say I've just tried the Alpha version, and it looks brilliant.
The only feature that I regually use on my email client(s) which it doesn't have (which I can't see on the roadmap) is mark as read button (next to, for example, the delete icon, etc); for example, select all the messages in a folder, and mark them all as read - handy once filtering messages into folders, etc.) - sorry if it is there and I can't see it!
Hope this was helpful, and I look forward to seeing future versions.
Many thanks,
James.