Recs.
Updated
SpecsUpdate
Pros
Pro Extremely powerful search features
While most email clients support searching content from their To, From and Cc fields, MailMate lets users search down to the different sections of these fields. For example, you can search for the address only, or the name only, or even any one of the embedded headers. Subjects can be searched by prefixes, or by specific words which may be contained within and so on.
Pro Markdown support
Markdown is a way to format text quickly using only the keyboard. Different text characters create different text: for example, putting asterisks (*) around a word or group of words will italicize them, while double asterisks (**) will bold that text. Markdown is a basic formatting system that can then be adapted to HTML or other formats.
Pro Clean, no-fuss interface
MailMate's UI is very basic. The icons are limited to some default MacOS standard folder images and the interface is very clean and simple, showing only what's needed without any fuss or distracting colours. Instead, opting for a mostly grey interface, with a sprinkle of some other colours here and there.
Pro Nice tagging support
One can define tupels of IMAP keywords and tags (which are shown in UI). In case of Gmail one can define triples of IMAP Keywords, Tags, and gmail lables.
(in Thunderbird one can only define the tags, whereas the corresponding IMAP keyword is not user-definable.)