Larger ISP's use an anti-spam agency called Spamhaus to protect their users from receiving mass email spam. Spamhaus uses spam traps and honey pots to gather data on IP addresses that are sending using email blast software. The spam traps and honey pots are fake email addresses that do not belong to any individual person but rather belong to an anti-spam organization. Once you are detected by one of these emails added to your list, you can become blacklisted. Becoming blacklisted prevents you from sending bulk email to ISP's.
Spam traps are generated typically by old email addresses. The ISP will deactivate an account after an extended period of inactivity. This will cause the email to show as a bounce. These bounces should then be removed from your list because of what the ISP does next. The ISP will reactivate the account without the user being able to log in. They will receive the emails and use the email address as a spam trap. Any spam that is sent to them will get the IP blacklisted and unable to send to that ISP anymore.
Two easy steps to prevent spam traps and honey pots are:1) Never purchase a list
Not everyone is able to do this. With bulk email marketing, you will be purchasing email lists or gathering them yourself without double opt-in method. It is key to use an ESP that will replace the IP's, servers and domains that they provide you free of charge if they become blacklisted. You must also choose an ESP that is designed for mass email marketing and not for white listed double opt-in data. Those ESP's that send to double opt-in white lists will shut you down immediately.