Never found a GUI mail client I didn't hate.

I use thunderbird only when I have to deal with incoming html emails. I use it on various platforms.

Alpine is by far my favorite client. Works especially well on high latency, low bandwidth connections. It is light weight but has alot of power for managing messages. I use it on all the various platforms I deal with. On the down side there are some imap servers that Alpine seems to hate when it comes to marking deleted messages only to have them immediately deleted. The lack of a deleted messages or trash folder will sometimes bite you. Once you expunge, the messages are gone. Gotta love those empty body calendar invites that Outlook sends.

K-9 on android is the best I've found although I recently ran into a problem with file attachments. It won't display certain types of files for attaching. You have to use an external program to select those types of files. Kinda kudgey.

Once a year I get to zero inbox.

I agree with the durability comment. We have used Kensington trackballs for years but their longevity has steadily deteriorated as the newer models have been released. The latest optical versions are the worst yet. We experience tracking problems and micro switch failures far too early in their life span. Kensington used to be much easier to deal with on warranty issues, basically no questions asked. Now they are asking for all sorts of purchase documentation to get replacements. We no long use trackballs as a standard piece of equipment.