Spam traps are email addresses used by Internet Service Providers (ISPs) and blocklist operators to identify senders who aren't following email best practices. These spam trap email addresses may have been legitimate at one time, but are now abandoned or invalid.
For example, if one of your contacts got a job at a new company, their old work email address would become invalid. Any contact that hasn't opened or clicked an email from you in over a year could be a spam trap and should be removed from your contact lists.
The impact of spam traps varies depending on the type. Hitting a pristine spam trap is more severe than hitting a recycled trap. If you've emailed a pristine spam trap, your domain or sending IP address could be immediately blocklisted. If you send email to recycled spam traps regularly, you could start to see your emails being routed to the junk folder. To avoid spam traps, be sure to regularly clean up your contact lists.