New
To combat a growing problem of users flooding queues with invalid recipients / invalid recipient domains (usually due to things like blog or forum registration sending confirmation emails), we create a list on each server that is populated with invalid recipients or invalid recipient domains that users on that server attempted to send mail to. Why we chose this path is a long story, however the problem doesn't seem to be shrinking much, and so we've standardized the list across all servers: https://github.com/mxroute/da_server_updates/blob/master/exim/spam_recipients