Hi everyone. I have a customer using SM 17x. He migrated one of his domains to O365 for email services, however, his customer wanted to continue to use the SM server as an antispam gateway because he loves the job that Declude/Message Sniffer/ClamAV and Cyren does to keep spam out of his inboxes. 

I would usually set up an Incoming Gateway in SM for this and use the Domain Forwarding option, but since Microsoft has 6 ranges of O365 IPs, using the Incoming Gateway/Domain Forwarding option was not working as needed. Instead, I had to follow the instructions at the link below and it works like a charm! I'm sure a lot of you already know this info, but for those of you who did not I thought it would be helpful. Enjoy!