Relaying now will be possible only through engin.umich.edu, and only for hosts in authorized domains. All relaying through lab hosts has been shut off. Authorized domains now include all university-related domains. The CAEN email hubs formerly permitted anyone anywhere on the Internet to connect and send email to anyone else on the Internet. This security hole was often abused by spammers relaying mail to their victims.
Spammers are people who flood user mailboxes with irrelevant or inappropriate messages.
For example, a user who works at a Detroit area company sends advertising email to a list of non-University email addresses. This mail spam then gets routed through a CAEN email hub. Once this happens, CAEN is viewed as responsible for the spam for having relayed the email. As a result, several users report the incident to anti-spam organizations in an effort to block further spam incidents from occurring. These anti-spam organizations target and restrict mail servers that permit third party relaying.