What is your favorite lightweight email client for Windows?

People still use offline email clients?

I guess of the windows email clients I've seen, and after looking over your examples, I'd say that Claws Mail looks pretty good. I've used the Zimbra Desktop Client with a Zimbra Collaboration Suite account and with a POP3 account. It worked for me at the time.

Thunderbird is nice, because it allows you to curb your top-posting habits, and it has an open plugin architecture like Firefox.

My favorite email client of all time is Pine/Alpine, but for a lot of people, this isn't a good tool because they 1) get way too much email 2) have a hard time filtering and/or deleting their email, and then Pine gets cluttered and unusable. I just liked that I could spam the "d" key and mark messages as to-be-deleted very quickly and easily.

My 2nd favorite email client was Eudora 3, because it was almost as simple as Pine. No IMAP support, no HTML email (a plague upon the virtual land). You couldn't even set up more than one account. Awesome.

These days I just use the Zimbra web client for work and the Gmail site for personal mail, combined with an aggressive amount of filtering and deleting.