In light of the Okta news, here are some statistics on 52+ character usernames (or UPNs in Azure) I've enumerated in Azure, to give an idea of what makes a long UPN and how common they are. Out of 53 million UPNs I've collected, only 1438 individual UPNs are 52 characters+ (0.003%). Seems to be pretty rare, but could always be skewed based on my particular username lists. If a full UPN is considered, it's not just the traditional 'username' aspect that contributes to its length. The main cause of these long UPNs is that they are configured at their '[tenant].onmicrosoft.com' domain. 423 of 464 domains where UPN exceeded 52 were '.onmicrosoft.com' tenant domains. The most common username that contributes to long UPNs is 'administrator', being found in 64% of the domains. I've included the counts by length of the pre-domain usernames, and the domains, where the overall UPN was 52 chars+.