SUMMARY

How to test if a mail server is open for relay.

DETAIL

Several anti-spam sites provide open relay query tools . 

MailEnable has an open relay utility provided at http://www.mailenable.com/Tools. This utility will attempt to relay through the server and will report if the server allows unauthorised use.

Other tools are available at http://www.dnsstuff.com and http://www.dnsreport.com

MORE INFORMATION

What are the best relay settings to use?:http://www.mailenable.com/kb/content/article.asp?ID=ME020001

Has the server been spammed through open relay?:http://www.mailenable.com/kb/content/article.asp?ID=ME020339

How does MailEnable determine who can relay?http://www.mailenable.com/kb/content/article.asp?ID=ME020034