I just installed it today because I was tired of apple mails mandate that I must block remote files 100% if the time (forcing me to click each time I want to see "load remote content") or let every random email I receive and preview have user tracked remote content (or the zero click bad stuff..). Thunderbird is much better at making this a balanced approach that's works well for me!
MailMate is a great option on macOS.
Agree, it’s great. Only disadvantage: no “Dark mode” for email content.
Thunderbird has the Dark Reader addon, which is very nice…