A spamtrap is an email address created specifically to lure spam. The spamtrap email address is typically hidden from human view in such a way that only an automated email harvester (used by spammers) can find it. It's then assumed that any emails sent to this address are considered spam.
Sending email to a spamtrap email address can harm your deliverability immensely. Your mail server IP or domain could be added to numerous blacklists. The major email providers (Gmail, Yahoo, Hotmail, etc) could start delivering all your emails to the Spam folder. The negative effects go on and on.
The most common way that honest marketers end up with spamtraps on their email lists is by purchasing email lists. You don't know the complete history of the list you purchased. You can't be 100% certain that the list has been cleaned and every subscriber is a human who genuinely wanted to join the list. This means that bought lists are frequently "infected" with spamtrap addresses.
Role accounts (ie. admin@, support@, webmaster@), although not "pure" spamtraps, can also carry a penalty. If an ISP goes out of business or is bought by another company, the new owner may decide to recycle those addresses as spamtraps. The penalty for sending to these addresses is lower than a pure sandtrap, but it's still something to watch out for.
There's a few ways you can detect and prevent Spamtrap issues:
This is pretty serious, but not the end of the world. One way you can help recover your reputation is to reconfirm your list by sending an email notification to all subscribers to re-subscribe. This will likely reduce your subscriber count by 3/4 or greater, but at least you'll know your list is clean/safe at that point.
Kane Miller from Winning.Email
Kane has a background in computer engineering, but now focuses on creating new and interesting web services. His passion for improving his own email deliverability rates was the driving force behind the creation of Winning.Email.