Note that the download also works as a 30 day trial version of MailMate. You can use the “Buy Now” link above or the “MailMate ▸ Registration” menu within MailMate if you decide to buy a license key.
You can fetch the latest beta release using the Software Update preferences pane within MailMate (release notes). Beta releases are usually quite stable.
Older Unsupported Releases
MailMate for macOS 10.7: MailMate 1.9.6 (r5318)
MailMate for macOS 10.6: MailMate 1.7.2 (r4587)
MailMate for macOS 10.5: MailMate 1.4.2 (r2818)