filtering out the, ahem, "idiots"
Not relevant to this specific case, but: For smaller companies I've found that "I got your phone number from your domain whois" is a very effective shibboleth.
The real effectiveness comes from having it here on HN (or other popular techie websites). There are enough employees lurking that someone will notice.
Works for most large companies, not just Microsoft.
But yeah, I do understand the challenges that are attached to having a very very large user base. There's no realistic way you can handle this in a great way for every person reporting a bug once you have 10M/100M/1000M MAUs.
Maybe machine learning can be a help here? At least in filtering out the, ahem, "idiots".