Some tools to check mail exchangers or verify mail addresses
Applications
.rbl
Check if your host is listed in one of ~150 different real-time blacklists. But please do not contract us if you are listed, don't blame the bearer..relay
Is your MX an open relay? A classic test ;).vrfy
Verify a given E-Mail address as good as possible without sending a confirmation message..surbl
Check if your host is listed in a spam URI real-time blacklist.