A machine is said to have an open mail relay if it is willing to transfer mail where neither the sender nor the recipient is a local user. Spammers use open relays to deliver their junk mail to recipients who have blocked mail from known spammer locations.
Below are links to more information about open mail relays and how to close them.
- Indiana University Knowledge Base: What is an open mail relay?
- MAPS Transport Security Initiative
- Coalition Against Unsolicited Commercial Email
- Resource for the freeware version of sendmail
- Prevent SMTP Relaying on Exchange Server
If after consulting the above sources you still have technical questions, contact:
