a) What is an Open Relay?
b) Why do open relays represents a problem?
If your mail server acts as an open relay, anyone could access it and pass spam (unsolicited commercial email) through your server.
Not only could this overload your server but it could damage your reputation because it will appear that you sent the spam.
As a result, your server may be blacklisted by other Internet Service providers in the world. Once blacklisted, none of the email that sent via your server can reach these ISPs.
c) How do I find out if I am running an open relay?
Network Abuse Clearinghouse provides a mail relay testing service on their website which runs in two modes.
- Anonymous mode sends commands to the server to be tested but doesn't actually send any mail. This can report false positives, hosts that appear to be open relays but actually aren't because they reject or discard a message after appearing to accept it.
- Registered user mode attempts to relay a message through the server to be tested. You must be a registered abuse.net user, and the relayed message will be addressed to you. If you're testing a server that accepts mail for your e-mail address, abuse.net can generate a temporary alias in the abuse.net domain that will be forwarded to you.
Simply filled up the web form to let them test your system.
d) How do I close my Open Relay?
MAPS compiles an extensive list of resources on how to secure your current mail system against third-party relay (open relay).
You may also access the spamlinks website to have access to relevant materials on:
- How to prevent unauthorised third-party mail relaying through your servers
- Filtering open relays can help to slightly reduce your spam load
- Tools to test for open relays
- Honeypots can be used to trap a spammer in the act of abusing an open relay
e) Where can I read more about Open Relay?