iOS 15.7

Running postfix/dovecot on Ubuntu 20.04 with LetsEncrypt Cert

Ports 25, 465, 993 forwarded through Mikrotik router to the Ubuntu box

Outlook is working fine, can send/receive email - initial imap account setup completed without any issues.

iOS mail app simply refuses to connect to the server, hangs on verifying for a long time during initial account setup, times out eventually and gives the option to save settings anyway - so I do that and then try to edit the account to put the correct settings in - selecting SSL along with the correct ports 993 for imaps, and 465 for smtps - again stuck on verifying and then throws an error "the imap server is not responding" yada yada.

Now this is where things get interesting, on the Mikrotik router there are no packets received whatsoever on ports 993 or 465 when trying to setup the iOS mail app - so the iOS mail app is simply making no attempt to open a tcp connection to the server.  It really does look like the iOS app is broken.  Just prove the ports are not being filtered somewhere, I manually connected to http://<my_ip>:993 from the phone and could see packets hit the Mikrotik.  Why Apple devs haven't fixed something so obvious with the mail app is beyond me.  Even if the certificate was bad, you'd still see packets hit the router during the initial handshake attempt - in my case there's absolutely nothing coming from the mail app.

Has anyone else encountered this?