This one happened to me two years ago:

Off on holiday overseas, just arrived and decide to check my Emails. Easy peasy..."Hey, we noticed you're logging in from a different country. We sent a security code to your backup account."

Welp, fine, login to my backup account: "Hey, we..." Can anybody guess the problem here? Yep, my primary account was the backup account for my backup. Lovely circular dependency.

Microsofts solution: Play the guessing game, where you name us Emails, Contacts and Folders to prove it's yours and we might unlock your account... or not (managed to get it back on the 2nd try)

Thank you Microsoft for ensuring my workfree, email-free holiday.