I'm using dovecot. I'm having a hell of a time with some versions of Outlook not being able to log into my server over port 993. These clients have to use port 143 and with
ssl = required and
disable_plaintext_auth = no. I've tried every encryption setting with Outlook (SSL/TLS, STARTTLS, Auto) but none work. I can't get any other combination of settings to work.
What's weird is, other versions of Outlook work fine over port 993 on the same machine. For example, the latest version of outlook that comes with MS 365 works fine.
Any ideas what I can do to get 993 working across all versions of Outlook?