ISPs and email inbox providers hate spam. They try their hardest to prevent it ever reaching their users. Spam traps are used by organizations to pinpoint spam accounts that can then be blocked or blacklisted - or both.
What is a spam trap?
A spam trap is simply an email address an organization creates and monitors. What makes them different to the average email address is that they should not find their way onto a mailing list.
Spam traps are never submitted to mailing lists and never used to subscribe to any services or send mail. They're clean. There's no way any organization should be sending email to these inboxes. Well, there's no way that can happen if the organization is only sending mail to legitimate addresses they have permission to use.
Where the problems begin...
If a marketer buys a mailing list on some shady forum, randomly scrapes addresses from the web, or otherwise grabs email addresses without asking permission, it is possible their list may well contain spam trap addresses. When an organization sees an email that originates from the marketer's domain in their spam trap, they come to the obvious conclusion. The marketer is a spammer.
In reality, there are a number of ways a spam trap address can end up on your mailing list. Perhaps a malicious subscriber dropped a spam trap email address into a subscription form on your site. Maybe they wanted to access premium content on your site but didn't wish to give their real email address. Or perhaps they made a typo.
How can you protect your sender reputation from spam traps?
All of these circumstances are avoidable if you're properly carrying out double opt-in email verification — and that's exactly the point. Email receivers want to punish organizations that aren't following email best practices.
If you have a spam trap address in your mailing list, the consequences can be unpleasant. Your domain's reputation as an email sender will be negatively impacted, making it difficult to get email delivered. If you're unlucky enough to hit a spam trap run by one of the anti-spam blacklist providers, you'll be blackballed by potentially dozens of organizations.
Make sure that every email in your mailing list is genuine. If you provide email services to third parties, use a spam filtering service capable of identifying potential spammers among your users and take action to stop email that comes from your domain hitting spam traps.