We have received numerous reports of spammers intentionally sending mail to the lowest priority (backup) MX records in an effort to bypass spam filtering. This problem can be added to when AppRiver's servers intentionally block IP addresses at the SMTP level due to excessive invalid delivery attempts and directory harvest attacks which causes the offending server to failover the next priority MX records. If you are seeing spam that is getting delivered directly to your server and bypassing AppRiver, we recommend that you take out any backup MX records that do not route through us. We have backup MX records available that include spam filtering.
Please send an email to firstname.lastname@example.org to get it setup for your domain.