The campus mail relays handle most of the email coming into and leaving campus. The relays run Debian GNU/Linux with Postfix as the mail transport agent. These servers do spam and virus detection with a host of utilities including several RBLs, Amavis, SpamAssassin and ClamAV. These services are provided free of charge to all departments at OSU.

The maximum size limit for a message sent through the campus mail relays is 100Mb.

Any device on the OSU network that needs to send mail can use the host as its outbound SMTP relay.

Until 9/17/2020, off-campus hosts could use with authentication as an outbound SMTP server. We are now recommending that email clients be configured to use or instead. For steps, see: Send Mail via POP/IMAP Client

Mail servers on campus should route outbound mail through instead of We try to divide up our traffic so that spam or virus mail inadvertently sent from workstations doesn't cause our production mail servers to be blacklisted. Please don't use to relay mail from regular workstations.

Note: the servers are inaccessible from off-campus. This allows us to handle on-campus and off-campus mail differently.

Please ensure mail servers have '' configured as a smarthost. For details see: Unix Host Mail Configuration - On-Campus Server (This link restricted to IT Pros)

Most inbound mail for campus passes through the servers. If you would like to point an MX at, please contact Network Engineering so that we can configure the necessary transport records.

Access Lists for Mail Servers

If you would like to configure a host to accept mail only from the campus mail servers, please allow the following IPs:

  • OSU Mail Relays:


Mail Flow Diagram

The diagram below shows how mail flows at OSU.  Click on the diagram to see the full-sized image.

Note that emails from authenticated clients, on-campus clients, and OSU mail servers are only subject to anti-virus scanning. In contrast, messages from the Internet (cloud with angry eyes in the diagram) are subject to many more checks including RBLs, greylisting and SpamAssassin tagging.

When email messages leave the OSU network destined for the Internet, they are subject to anti-virus scanning, but are not otherwise hindered.

The "Client Rules" on the top-right of the picture show that email can also be filtered by the recipient.

Diagram showing email flow at OSU