How it works
You've given it the login details for an email address, there's a cron entry that will run once a day. It connects to your mail server and looks at the headers for all the emails in the inbox (so don't have lots in there!).
If any of the headers make the email look like a bounce message, it will download the email and process it to find where it was originally sent to and if it's a failure that should affect the user.
If it is, it'll look for users in your community with that email address and update their user status to Email Invalid (Bounced)
or User awaiting confirmation (from edit)
depending on the version of XenForo you're using.
- It will scan all emails available via POP3, it may hang if the connection to the mail server is slow or there are lots of messages (PHP will kill it)