Spam traps are a method of fraud management used by major Internet Service Providers (ISPs). They are used for blacklisting spammers so they can block emails from them. A spam trap appears to be a real email address, but it doesn't belong to a real person and can't be used for any kind of communication.
Basically, they are phony email addresses dropped around the internet as bait for robots and harvesters of email addresses that in turn sell the mailing list to others. If one of those email addresses winds up in your list of subscribers, it has poisoned the well, so to speak.
This is a reminder that using an email service that validates the subscriber through user action is not only necessary for determining their interest but also to maintain your list with humans without having any tampering beyond your control. It is also an alarming message that purchasing a mailing list from another party is a dangerous action to take. If you purchase a poisoned mailing list, you can infect your existing list and find yourself in deep trouble.
Source: Kelly "Rags" Ragland