Why is an open relay bad?
Spammers are constantly on the lookout for open relay SMTP (Simple Mail Transfer Protocol) servers. They use the open relays to send unsolicited mail to a large number of email addresses, which has an impact on delivery speed, bandwidth, disk storage space, CPU processing and more.
A number of organizations are cracking down on spam originating from open relay servers by forming blacklists. Several anti-spam solutions check if the mail server is in one of these blacklists before allowing incoming mail from it. If your mail server gets listed on one of these blacklists, a lot of the emails that you would be sending would not be reaching their destination.
OPEN RELAY ONLINE TESTING
Abuse.net relay testing – www.abuse.net/relay.html
Anonymous Relay Test – www.antispam-ufrj.pads.ufrj.br/test-relay.html
Anonymous Relay Test – www.aupads.org/test-relay.html
Third Party Relay Check – www.rbl.jp/svcheck.php
Open Relay Tester – www.mob.net/~ted/tools/relaytester.php3
SpamHelp.org SMTP Open Relay Test – www.spamhelp.org/shopenrelay/