Spamblocker causing 571 Delivery not authorized errors?
We have this ongoing sporadic issue that first started a few months ago whereby certain external contacts keep receiving NDR messages with '571 Delivery not authorized, message refused' as the reason for the delivery failure.
Whenever we rebooted the fireboxes the issue would disappear for a while, only to then re-occur later.
We are using an M370 Firebox cluster and recently updated to fireware OS V12.4.1 Update 1 but the issue persists.
After adding a couple of the affected domains to the 'ignore' list within Spamblocker they have been able to send mail successfully.
Is this a known issue? Are there any workarounds for this?