Starting with the Shasta release, Rocks has moved to the Postfix mail server for cluster-wide email service. RedHat, Apple, and most other Unix-based OSs have switched from Sendmail to Postfix in recent years. Postfix is much easier to configure than its predecessor, a welcome fact to most administrators. Postfix also has more advanced security features and better performance than Sendmail.
In Rocks, the frontend serves as the mail relay for all cluster nodes. This means that compute nodes send mail to the frontend, which forwards it to the outside world.
You can view the mail log on the frontend in the file /var/log/mail. Here postfix keeps a record of all incoming and outgoing email messages.