I don’t think it’s reasonable to trust the mail server to have perfect filters. Systems like this have to be designed assuming realistic error rates and failure

I don’t think it’s reasonable to trust the mail server to have perfect filters. Systems like this have to be designed assuming realistic error rates and failures, and part of that has to be asking questions like whether the resulting UI will lend an attacker more credibility than they would have or whether the tool should be surfacing information which people miss such as telling you that you’ve never received emails from that domain before and your normal M365 interactions use Microsoft.com.