Having your server blacklisted by a major ISP can seriously disrupt service for your business. Many people use free email accounts at AOL, Microsoft Live, Google and Yahoo. If one of them identified you as a spammer and began blocking your email, you would have a tough time doing business with many of your customers.
To reduce the chance of getting blacklisted, it is important to be familiar with their spam feedback services and follow their bulk sending guidelines closely. Though they do not publish their blacklists, many major ISPs provide guidelines for senders of large newsletters to monitor their email. Even if your newsletters are opt-in, you must follow the ISP’s bulk sender guidelines to assure delivery of your email.
Each major provider handles these issues a little differently. Fortunately, they all have websites that describe their policies and the tools they have available. To get a list of the tools at some of the major email providers, check out this great article at rackTIPs: