I tried to stick with the native mail.app but found it to be buggy and broken in too many ways to be usable. Airmail seems to be working fine for me and doesn't seem to be abandoned.
Perhaps it depends with what services you use it?
Personally I've only ever used it with Apple's iCloud's mail service which worked great but didn't support custom domains. I also used it as a POP client for Gmail (mostly because Google's IMAP support initially was horrible and their tags didn't play well with IMAP folders back then).
I can say though that FastMail's IMAP service works flawlessly for me, and so does the mail.app client for it.
Yes, Airmail is still supported, but IMHO its UI suffers from severe feature creep. I also found it never reliably notified me that account passwords needed to be changed. I used it against MS Outlook, and whenever the password on the backend needed to be changed after 60 days, Airmail would simply sit there and not receive any new emails.
Yes, Airmail is still supported, but IMHO its UI suffers from severe feature creep. I also found it never reliably notified me that account passwords needed to be changed. I used it against MS Outlook, and whenever the password on the backend needed to be changed after 60 days, Airmail would simply sit there and not receive any new emails.