University of California, Riverside

C&C Antispam

Will Graylisting Block Legitimate E-mail?

Computing and Communications believes, based on our research and on the design of the graylisting system, that it is very unlikely that any legitimate mail will be ultimately prevented from delivery. Graylisting works by taking advantage of characteristics of the SMTP protocol that is the universal standard for mail delivery over the Internet. While graylisting does initially reject mail from previously unknown senders, properly configured mail servers forwarding legitimate mail will simply resend the e-mail after a relatively short delay. Please note that e-mails from UCR users on campus will be automatically passed by the graylisting system and are thus unaffected by it.

However, it is possible, though unlikely, that the mail server at a remote location could be improperly configured and thus either fail to resend the message altogether, or resend the message either too soon or after too long of a delay to be accepted by the graylisting system. In this case, the message would continue to be rejected, and ultimately the remote mail server may cease delivery attempts.

Even in these unlikely circumstances, the remote mail server will typically notify the user sending the e-mail that it has been unsuccessful in its delivery attempts. Thus, the person sending the e-mail will be aware of the fact that you did not receive his/her message, and may contact you by other means.

If you are notified by an individual off-campus who says that his/her e-mail to you was bounced/rejected, please contact Phyllis Franco (, Manager, Computer Support Group.

More Information 

General Campus Information

University of California, Riverside
900 University Ave.
Riverside, CA 92521
Tel: (951) 827-1012

Department Information

Computing & Communications
Computing & Communications Bldg.

Tel: (951) 827-4741
Fax: (951) 827-4541