You've not worked in large companies then because people end up having the same first and last names as each other. Collision with names is literally unavoidable in large companies. Also for people who don't have a single last name, it can get confusing. Do you do First.Last.Last@company or just tell them to pick a favorite last name? (Which is potentially difficult for some people for personal reasons.) Honestly, just give people a chance to tell you what they want to be called, and this all smooths over.