BoxTrapper functions as a spam filter for email addresses. The filter works through "challenge-response" verification. When an email is sent to an account that has enabled BoxTrapper, a verification email is automatically sent in response. This verification email requires the original sender to reply to the verification request, leaving the subject line intact. When the reply is received, the original message will be delivered to the intended recipient's account.
The goal in enabling BoxTrapper is to block BoxTrapper emails that will not reply to the verification email. Mail box aliases will allow you to setup multiple email addresses to go to a single mail box.
Note: When BoxTrapper is enabled, even when automatic whitelisting is disabled, any email address that you send email to will automatically be added to the whitelist, allowing email to be received from that address without an authentication process.