Function microsoft_hop 

fn microsoft_hop(received: &str) -> bool

A hop between Microsoft 365’s own servers: received by one of the names they carry between themselves (MICROSOFT_INSIDE). Those hops pass the message from one public address of Microsoft’s to another, so an address cannot tell them from where the message came in, which is the hop received by its Internet frontend, *.mail.protection.outlook.com (“Received: from mail.sender.example (203.0.113.25) by BN8NAM12FT034.mail.protection.outlook.com (10.13.182.135) with Microsoft SMTP Server … via Frontend Transport”). The receiving server writes its own name, and the lines above where the message came in are Microsoft’s: no sender writes one of them.