You need to test whether or not SMTP authentication is working with Symantec Messaging Gateway.
telnet <SMG_IP_address> 587
EHLO mailserver.com
AUTH LOGIN
334 VXNlcm5hbWU6
dXNlcm5hbWUuY29t
334 UGFzc3dvcmQ6
bXlwYXNzd29yZ$4
Note: If you receive an error from this point forward, double-check the password and encoding.
If you need to manually convert the username and password, search online for a base64 encode and decode tool.