I am working with a client who's company is splitting in two. They now have 2 hybrid exchange environments set up, and are just beginning to migrate mail from one to the other for the users who will be joining the 2nd company.
They have mail forwarding turned on for the users who have accounts on the 2nd system now, but a lot of it is being marked as spam by the 2nd EXO tentant.
What I think is happening is that the 2nd tenant is looking at from domain names and saying that the system sending that email, (the original tenant), isn't what's listed as a sending domain name, (SPF records and all that).
How can I set up a rule that says anything that goes from Tenant A is whitelisted on Tenant B? Regardless of whatever domain it came from? If it doesn't get marked as spam on Tenant A then I don't want it being marked as SPAM on Tenant B.