MAIL not accepted from server
Because of the spam abuse that has historically been sent from people using EC2 instances, virtually ALL popular mail providers block the receipt of email from EC2 instances. The world of email and anti-spam measures is part-technical, part-political. For this reason, AWS offers Amazon Simple Email Service.
AWS works with mail providers to ensure that the nodes used by SES have been whitelisted because we do proper authorization/verification up-front.
In this case, the ability to send email from one server but not AWS is, in all likelihood, due to EC2's IP range being blacklisted by Google.
If the same user/pass works elsewhere without changes, I'm not sure what to say. I know that lots and lots of mail traffic no longer uses port
25, opting instead for
587 for non-SSL and
465 for SSL. That's the first place I'd start poking to find a solution.