We have been testing new applications and noticed that some users are having issues using Mandrill on our servers. We are writing this article to help our resellers and community members to resolve a common issue.
We found two points of failure for people who use cPanel as their control panel system.
Restrict outgoing SMTP to root, exim, and mailman (FKA SMTP Tweak) Enabling this feature will redirect outgoing SMTP connections to the local mail server. root, exim, and mailman are still allowed to make direct connections.
This setting can be found in Tweak Settings in WHMCS by cPanel.
As extra protection we enabled CSF Firewall SMTP Block and only allow specific users access to SMTP out on ports 25,465,587 when using Web applications and custome scripts.
Please contact support if you'd like your account to support Mandrill and we will gladly help you.