Too many unknown recipients from this host

Remote hosts which consistently attempt to send messages to email addresses that do not exist on our mail servers will be temporarily blocked.  This is done to protect our mail servers from abuse such as a dictionary attack .  As long as such activity continues the remote email server will remain blocked.  If the activity stops the blacklist entry will be automatically removed.

If you get this error message when sending mail to the ABI Hosting email servers, you may want to ensure that your mail server is not an open relay and that it is not relaying for compromised PCs.  Other reasons for getting this error message could be that an exploitable proxy or form-to-email script is running on the server, your email server is sending backscatter , or your server employs Sender Address Verification .  It is recommended that SAV be disabled, as the traffic generated from such a check is indistinguishable from abuse.