From the dovecot logs.

dovecot-info.log May 11 09:27:45 imap-login: Info: Aborted login (no auth attempts in 0 secs): user=<>, rip=192.168.0.1, lip=192.168.0.15, session=<pXcBJ8oVbgDAqAAB>

dovecot-debug.log May 11 09:27:45 auth: Debug: auth client connected (pid=17388)

When I try to connect using either the iOS Mail app, or Outlook mail app, nothing happens at al with ssl, and if I use plain login the iOS device tells me I have either the username or password wrong - which I haven't.

Connection from Mac with MailMate works fine. iOS doesn't.

so I'm stumped. I can't see why this is refusing the connection.