Hello Jeff,
Thank you for sharing the access information.
I checked, and it seems your hosting provider may be restricting external SMTP connections. Do you have access to WHM?
If you manage WHM yourself, please check the following:
WHM → Security Center → SMTP Restrictions
Please disable SMTP Restrictions.
Also, please check the CSF configuration for:
SMTP_BLOCK
SMTP_REDIRECT
SMTP_PORTS
SMTP_ALLOWUSER
Please make sure ports 587 and 2525 are open, and that the website’s cPanel user is allowed to connect to external SMTP services.
Then please run these commands from the hosting SSH account, not as root:
Please send me the results, and then I can continue checking further.