I had to stop using Office365 for business because it kept doing this same thing. I disabled every spam, and protection I could find, and enlisted the help of support. Some legitimate email would simply never arrive and they couldn’t explain why. It seems there are layers of protection, some with no logging (available to the tenant admin) to troubleshoot, it became a huge waste of time, negating the purpose of using a cloud service. In the end I moved to a different service provider and never had the problem again.
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I had to stop using Office365 for business because it kept doing this same thing. I disabled every spam, and protection I could find, and enlisted the help of support. Some legitimate email would simply never arrive and they couldn’t explain why. It seems there are layers of protection, some with no logging (available to the tenant admin) to troubleshoot, it became a huge waste of time, negating the purpose of using a cloud service. In the end I moved to a different service provider and never had the problem again.