Recipient address rejected by Destination

Emails coming in to our domain are seemingly randomly being rejected with the reason: recipient address rejected by destination. The recipient addresses are valid, and we do receive emails to those same recipients through ASG. For instance, an email from Comodo was blocked for the same reason a few minutes ago, then I received one. Customers of ours are having difficulty emailing us, and this is bad for business, so please help.


What was the delay between you changing your MX records and these issues occuring?