Bumping. :-)
I'm having the exact same issue.
Just setup osTicket. v1.17.3 (ca95150)
I'm using a self-hosted mailcow. Version: 2023-05a with LetsEncrypt certificates that are not expired.
In fact I just got done configuring and setting up the default "support@" email address in osTicket and confirmed it could login to mailcow just fine:
Both SMTP and IMAP worked just fine.
Now I'm in the process of setting up a separate email address.
And when I go to configure the Outgoing SMTP parameters, using the same hostname, port, and authentication just I just got done configuring for support@ I receive the same "Host, Port, and Protocol Required" as OP received when they opened this thread initially.
Except, I am the systems administrator :-) and I'm not using a self-signed certificate anywhere. There's no firewall that's blocking IMAP or SMTPS connections and I confirmed that everything was working just fine for the initial support@ configuration, it's only when I've just now gone in to configure a secondary email address where I've run into a problem. :-)
Would appreciate any thoughts or ideas anyone would have to resolve this.
Thanks!