Will there come a time when you can only email people who use the same ISP you do? It sure seems like it when the ISPs blacklist each other. Smaller ISP block mail from Roadrunner, Earthlink, AOL, and Hotmail, Yahoo or other free mail services.

If you'd like to see if your IP address is on an RBL, go to http://www.openrbl.com/ and enter your mail server's IP address. If you use any major ISP, you're probably on at least one list. To find your SMTP server's IP and you use a POP3 or IMAP account, send yourself a message, then right click on a message and choose options. The server's IP is in the lowest Received line in the header. You can also check the IP used by your internet connection, although if you don't run your own SMTP server, it won't matter if it's blocked.

My IP is blocked on several vigilante lists because the IP is provided by Sprint and Sprint is considered spam friendly. Sprint partners with Earthlink so I could use earthlink mail servers, but they are also blocked on a number of vigilante lists. I keep a myrealbox.com account and send using their SMTP sever.

If you're an administrator looking to control spam, of all the commercial antispam applications I've reviewed, I like NEMX the best. It offers a lot flexibility and control. Spam Assassin is also very good from what I'm told. Neither relies solely on black lists and when properly configured, have a very low false positive rate. Exchange server includes domain blocking as well. Home users have a number of excellent antipsam programs to choose from, including MailWasher and CloudMark's Spamnet.

I could write a book on spam prevention. Maybe I will when I'm done with my current book...

Diane Poremsky is the president of CDOLive LLC and a Microsoft Outlook MVP. She's coauthor of Word 2002: The Complete Reference (Osborne, 2001) and Beginning Visual Basic 6 Application Development (for Wrox Press). For questions or suggestions for future columns, write her at outlook@cdolive.com.