I have a test box with 4 Instances of SQL Server on it. One 2012 instance and three 2008 R2 instances.
Database mail works fine on one of the named 2008 R2 Instances but not on any of the others.
I've been going through the troubleshooting steps on Microsoft's website and everything checks out. All of the settings are correct and it's starting just fine, it just won't send an email.
The profiles are public and the logins have the appropriate permissions.
The mail log contains:
Log ID 9137 Process ID 7740 Mail Item ID 6031 Last Modified 3/5/2018 11:34:23 AM Last Modified By sa Message The mail could not be sent to the recipients because of the mail server failure. (Sending Mail using Account 1 (2018-03-05T11:34:23). Exception Message: Could not connect to mail server. (A non-recoverable error occurred during a database lookup).
I have tried both sending the test emails through the UI (via Send Test Email), and through my own procedures. When I look in the database mail log I see the same errors stretching back to when I built the instances. I see messages in the log file about database mail successfully starting and shutting down.
I've rebooted several times and all of the settings are exactly the same between instances. One instance works perfectly and three others don't. If it were a firewall or AV issue it would more than likely be the same for all instances.