GW 2012 SP4

I am getting the following error for ALL users when sending to 2
domains :
sympatico.ca and bell.net


Undeliveable message includes : Response: 550 Sender address is invalid


This occurs for a variety of addresses to those 2 domains.


This may be related to the SP4 update but I'm not sure. Certainly,
before the update, we did not have this problem.

Steve