By default when the `spamtrap` alias is enabled for a virtual server, any email sent to it will be added to SpamAssassin's learning database for the user who forwarded it. However, this option can be used to also add the original senders of spam to the system-wide or domain-level blacklists.

This can be useful if you receive a lot of spam sent from the same address. However, since spammers often vary or fake the from address in email, blacklisting them is typically not very effective.