If you have Sender ID enabled on your Exchange server, it will block messages that SpamHero filters because it will not recognize SpamHero as being the authorized sender of the message. The following error message will appear in the delivery logs of affected messages:
550 5.7.1 Sender ID (PRA) Not Permitted
To fix this problem, disable Sender ID on an Exchange SMTP virtual server as follows:
1. Start Exchange System Manager: Click Start, point to All Programs, point to Microsoft Exchange, and then click System Manager.
If the above solution does not work for you, let us know what version of Exchange you are running, and we will check if an updated solution has been provided by Microsoft.