So the problem is that you can’t log in to the mail server–absolutely nothing you’ve posted gives any hint that there’s anything related to SSL/TLS going on, so I have no idea why you thought that was the case.
I wonder about the credentials you’re using, though. You’re using a hostname of pdc.something, which suggests “primary domain controller”. That’s ordinarily something that should resolve to your AD domain controller, which is a separate container (with a separate IP address from the Neth box). Is that the case? Because that will cause problems.
Otherwise, if pdc.whatever resolves to the main IP address of your Neth box, we’ll need to see what’s going on in a lot more detail. I thought Thunderbird would give that, but apparently not. So here’s what you’re going to need to do, from some sort of Unix-y (Linux, macOS, *BSD) client system, using the command line:
- First, use the first two Perl commands at this page:
https://www.ndchost.com/wiki/mail/test-smtp-auth-telnet
to get the base64-encoded username and password - Second, use
opensslto initiate the connection:openssl s_client -starttls smtp -crlf -connect hostname:587 - Third, follow the instructions at the link above beginning at
AUTH LOGIN.
Post the output of that session so we can get a better idea of what’s going on.
Edit: I’d think someone would have written a script that could test this, both on IMAP and SMTP, and show you where any errors are, but Google isn’t finding one.