Unable to connect to SMTP server requiring STARTTLS

Try ruling out SolarWinds and use powershell to test mail.

Also might be worth looking into what versions of tls are enabled on each server (both smtp and orion). 

https://docs.microsoft.com/en-us/dotnet/framework/network-programming/tls

https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.utility/send-mailmessage?view=powershell-7

The Centos box (mail server) allows:

Accepted TLS12 128 bits AES128-SHA256

Accepted TLS12 128 bits AES128-SHA

Accepted TLS12 256 bits AES256-SHA256

Accepted TLS12 256 bits AES256-SHA

Accepted TLS12 128 bits AES128-SHA

Not sure how to check what versions of tls are on the WHD box, it is Windows server 2012.

When trying to send an email from an open ticket I receive the error:

Could not send e-mail to USER <USER@USERDOMAIN>
due to the following error:

Could not create transport for E-Mail messages: Permission denied: connect

Also:

Encountered error while attempting to create transport for sending email: com.macsdesign.whd.util.EmailMessageController$CouldNotCreateTransportException: Could not create transport for E-Mail messages: Permission denied: connect

When checking the email history

Do you have any security software that blocks smtp mail messaging? I've seen some antivirus software block that by default.

Thanks a bunch!  A week of pounding my head against a wall, and McAfee is the culprit!

I'm blaming my colleague on this one, he built the server while I was on vacation.