Preventing SMTP Mail RelayDocument ID: 2153HQ
How can I prevent unauthorized SMTP Mail Relay?
A relay is a mail transport situation where neither the sender or receiver is a user in the local domain.
Relay restrictions are set in EIMS Admin using the menu selection: Admin:Preferences...:Relay restrictions. The most secure setting is the second choice: "Only relay if for local domains or the following domains AND if from a valid IP".
This setting is the most restrictive and may not work well if you have users connecting from domains outside the local domain.
Adding domains to the list in the Relay restrictions settings dialog to grant access to your "outside" users will also open your EIMS server to use by anyone in the domains listed, which could allow unauthorized usage.
Maintaining an adequate list of domains may be impossible since users will often be connecting from domains that are unknown at the time you are setting up the relay restrictions.
The best solution to this situation would be to use SMTP AUTH if the user is using a mail client that supports it. Information on how to enable SMTP AUTH in Eudora for Windows and Macintosh are provided.
Another way to get around this problem is to suggest that "outside" users use a SMTP server provided by the ISP they are using for their Internet connection.
To see which black lists you are on http://relays.osirusoft.com/cgi-bin/rbcheck.cgi
To check if you are open for relay http://www.abuse.net/relay.html
KEYWORDS: EIMS, SMTP
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