Spamtraps are email addresses used by ISPs, anti-spam organizations, and other groups as a way to find people who send to out-of-date lists, or lists they don't have permission to send to. Spamtraps look just like normal email addresses, and are often created from old email accounts that are no longer in use by their original owners. New spamtraps are created all the time, but since there's no real human on the other end, these addresses don't sign up to lists or result in any opens and clicks if you send to them.
How do spamtraps get on a list?
Spamtraps are often recycled from inactive addresses, which could already be on your list. When a list isn't actively managed, these unengaged, stale addresses stay on the list and may become spamtraps. Sometimes, spamtraps appear in publicly available data, which are scraped off the web by people who sell contact lists online. You definitely don't want this kind of data on your Mailchimp lists.
Why is this a problem?
ISPs don't typically give advance warnings when there's a spamtrap issue. Their first step is often to block our sending IPs, which is a big deal. A block to our sending IPs affects delivery for all Mailchimp users, and that's why we have to guard against spamtraps so carefully.
Unfortunately, ISPs and anti-spam organizations who run spamtraps don't provide which addresses they use, since sharing these addresses would defeat the purpose of the spamtrap. As a result, our Support Team can't find, provide, or block these addresses for you.
If you have an issue with spamtraps, don't worry as much about which addresses are offensive, and focus more on improving your list management practices. When you grow your list safely, regularly maintain your list, remove inactive subscribers, and ask subscribers to update their profiles, your rates of bounces, abuse complaints and unsubscribes will fall.
What can I do?
One effective way to maintain the health of your list is to prune inactive subscribers. This process also keeps your list cost-effective, by removing the "dead-weight" of un-engaged (and unprofitable) recipients. Since Mailchimp's Monthly pricing is based on list size, pruning the list helps to keeps your costs low, improving your ROI.
If your list is very old, has been inactive for a long time, or there could be issues with the way the list was collected, pruning the list won't be sufficient. Try to reconfirm the list, to ensure there is a real human checking the inbox who is still interested your content.