EDIT: Okay, gotcha on the dig command. I'm not sure if posting the output of that would be appropriate since the result of "dig" shows a bunch of different IP numbers, possibly some that belong to hardware from other people?
PLEASE, post the full result 
Thanks again. I'm going to have to wait until the morning to get more info. from our admin. I know that we used fail2ban in the past and we didn't have a problem with it before. Yes, we do have a firewall enabled, but that's on the home server and not the machines that my wife and I are working from. That#s why we're using the vpn on our work machines. Our connection is cable ethernet, but I'm pretty sure that our router has its own built in firewall. Will need to check on that later on too. When I have more information to provide, I'll be back. Thanks for everything so far. Have a great evening.
BTW ...
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As a small information here, some providers block the SMTP-Ports for "security reasons". You could try another network (e.g. open a hotspot with your smartphone and retry).
Some block both ports here in germany, very crazy..
Maybe it is a German Telekom Speedport Router. There is a SMTP whitelist on that Box.
Thanks for the assistance. Found the problem this morning after I tried sending a message with our VPN service disabled. That message went through without a problem to 3 different accounts. Then my wife sent a test message to 8 people from her machine, and that worked just fine too. We're using the default mail server setting in Thunderbird. Geez, can't believe something that simple was tried last ... 
I did mention the PIA vpn service in my third post though ...
Just out of curiosity, what is that external mails server setting in imscp for? Since I adjust settings in the reseller portion of the panel, it would be nice to understand why that should only be enabled under certain conditions? Thank you.
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