I felt the same, but it’s worth mentioning that you can make some small adjustments to improve how Fmail looks.
The status menu can be hidden, and the toolbar is customizable, so I just right-clicked and removed all the icons from it. Then, in the app’s settings (under User Interface), I checked the option to Adjust top bar colour to Fastmail theme. That tidies up the UI a bit.
The icon I just replaced with one from macosicons.com that was more to my liking.
And, in case it’s helpful, on the Mac you can use 1Password’s Universal autofill via Quick Access to autofill stuff outside the browser, like apps and system prompts.
I don’t see a single reference to SMTP on the page you linked to.
As far as I know only the Fastmail web interface allows selecting any previously used Masked Email address when composing a new email.
Were you able to persist those changes?
When I experimented with this I could indeed hide several things, but some of them (like the URL and browse back/forward buttons) always returned after restarting FMail2.
Yea, my recollection about reply-to was incorrect. Maybe from way in the past on a different OS. Dunno. I should have kept quiet. But does this help?
Again, ask FastMail support for the best advice. Even if you do not communicate with them, they have a lot of documentation available on their web site.
I’ve had no issues with those changes reverting on either of the two Macs I use Fmail on (even after frequent restarts of the app and computers), so I’m afraid I don’t know what to suggest.
I’ve been quite happy with the app, overall, though I’m mostly just biding my time until Mimestream launches IMAP/JMAP support.
As noted above, FMail2 is just a wrapper for the web interface and, thus, it too allows selecting previously used Masked Mail addresses when composing a new email. Highly recommended - developer is very responsive.