How can I keep my IP address from being blacklisted?

If you are using our service for outbound filtering, that should help. Here are some other tips:

• Via the network firewall, limit inbound SMTP traffic to the spam filter IP networks; this prevents spammers from being able to connect to your mail server to send out spam.
• Make sure you have a proper reverse 'PTR' entry in DNS for the IP address of your mail server. For example, if mail.yourcompany.com is located at 1.2.3.4 then your ISP (whoever controls the 1.2.3.4 IP address) should have a reverse DNS entry that points 1.2.3.4 to mail.yourcompany.com.
• Make sure anti-spyware and anti-virus software is up to date on your mail server and all workstations; this can prevent large spam runs from emanating within your network (often unbeknownst to the network administrator) and getting the mail server blacklisted.
• If conducting email marketing campaigns, use a third-party service like Constant Contact or Exact Target to send the messages rather than using the internal mail server. Also make sure that all recipients have opted in, and handle any unsubscribe requests promptly.
• When acquiring a new IP address to be used for the mail server, make sure it is not on any blacklists; if it is already on blacklists due to its prior history, request a different IP address from the ISP.
• If you are on a blacklist, follow that blacklist's specific rules for getting your IP address removed (see the web site for that blacklist). They are all different; some require intervention of the blacklist administrators, but many include web-based tools that allow you to remove your IP quickly and easily. If you conduct email marketing campaigns, be prepared to document how your recipient list opted in to receive emails from you.
• Make sure that your spam filter settings are configured to block email going to unknown recipients. Often, a spammer will spoof a phony "from" address when they send out a spam mass-mailer; if one of your domains is attacked in this manner, the bounce messages generated by the emails sent to invalid email addresses will go back to the spoofed sender, which may be a real address! If a legitimate mail server sees a high volume of incoming messages, even bounce messages, they may report your IP to blacklists.