I have now been using MailMate for about 10 month and I’m more than pleased with it. Everything good I wrote about in MailMate replaces GyazMail after four years is still true. The latest 64 bit beta build is rock solid and consumes less than 200 MB of RAM with 60000+ messages.
Four years ago I replaced Eudora with GyazMail and wrote about it in GyazMail replaces Eudora after 15 years and Two weeks with GyazMail. Now GyazMail has been replaced with MailMate. After moving all my locally stored mail to a local IMAP server switching mail client got a lot easier.