Are you on a mail server blacklist?

Mail server blacklists are insidious. Just about anyone can submit your e-mail address, domain or even IP address to a DNS blacklist (DNSBL). Once that happens, the chances of your messages getting through to people become pretty lousy. (A DNS blacklist is also known as a blackhole list.)

While certainly mail servers used by spammers should be on blacklists, how do the rest of us get there?

• Perhaps one of your machines been turned into a spambot zombie.
• Perhaps your mail server is configured as an open relay (bad, bad, bad!).
• Perhaps someone else using your ISP is a spammer.
• Perhaps one of your IP addresses was once assigned to a spammer.

What’s important is for you to find out if you’re on a blacklist. You should do this periodically. If you are on a blacklist, there are various resources available for getting yourself off again. But before you can do that, you need to know if there’s a problem.

Most corporate IT people only know if there’s a blacklist problem when one of their employees complains that his/her e-mail is blocked. However, you should be more proactive. If you host your own e-mail server, one free resource you can use is Blacklist Check, from MXToolbox, which checks your server’s IP address. If you don’t know the IP address for the domain’s MX records, they have a tool for that too, and another one for server diagnostics.

The company sells services to help you deal resolve mail problems. I’m not endorsing them; I’ve never even looked at them. However, their blacklist checker and other free tools are very useful.