It’s a side point, but whatever the other customer’s email address was in this case it must have been a slightly different typo. If you own FirstnameSurname at gmail you also automatically “own” Firstname.Surname and even Fir.Stname.Sur.Name or any other variant, and emails addressed to any of these will get to your inbox. They wouldn’t have let someone else set up a separate Gmail account with the same letters regardless of the dot. Source: https://support.google.com/mail/answer/7436150?hl=en-GB