Today we’ve added new filtering to mail submitted through our Outbound Mail (SMTP AUTH) service. We’ve never allowed submission of span or viruses through our outbound mail service, and previously we were using a combination of SpamAssassin and ClamAV for that purposes. The new addition is a commercial filter we recently subscribed to. We have also configured it to allow spam-containing submissions to a few select obvious recipient address patterns for reporting and troubleshooting.
If you encounter any issues with mail submission please contact support so we can look in to it.
Eventually this filter will make its way to the incoming side of our mail services, however that integration process is much more involved since it needs to be controllable through the account control center.
UPDATE 3/29/2016: We’ve removed this new filter due to customer complaints on mail submissions. We will be reevaluating our options.