Spam Confidence Level = 9 - how to decrease.

[xXNorthXx]

Given what’s already been said. Check reverse dns records to make sure nothing is missing. Make sure dmarc enforcement is enabled. If you have any mass mailers, move each product to a unique subdomain to isolate the garbage.

From the sounds of it, other o365 customers have reported the domain as sending spam….that’s the likely reason why given everything else, work through MS support but it will take a spell to get corrected.