I've been using KMail for many years. It suits me in many ways, the most
important of which being that I don't need to keep switching my hands
between mouse and keyboard. It has far more functionality than I need, but
then so it seems do its competitors.
The only problem is the fragility of the program. It does some very odd
things at times. Recently, for instance, while it's processing new messages
I've been seeing the number of messages in a folder jump very briefly to a
six-digit number. And it can't handle damaged messages imported from old
This week I tried Claws-mail. Creating and populating an MH folder structure
for it from my KMail directory were easy, and it looked as though it would
make a good alternative to KMail. But I can't do anything without the mouse!
And scrolling operates in the message list instead of the message.
Allegedly, the default key bindings can be changed on the fly, but that
excludes arrow and paging keys and who-knows-what else.
So it's back to KMail for me.