Field note: "This username may be incorrect"

A user tried to sign in to Microsoft 365 with her email address and got “This username may be incorrect.” The account existed, her email worked, and nothing looked wrong at a glance.

What was really going on

The office synced its on-premises Active Directory to Microsoft 365. In that setup, you sign in with your UPN (user principal name), which looks like an email address but doesn’t have to match it.

Over years of changes, this user’s UPN had been left as an old short form of her name (something like [email protected]), while her actual email address was [email protected]. People naturally sign in with their email address, which wasn’t her sign-in name at all.

The fix

Because the account synced from on-premises AD, the change had to be made there, not in Microsoft 365:

Set-ADUser jd -UserPrincipalName "[email protected]"

Then, on the server running the sync:

Start-ADSyncSyncCycle -PolicyType Delta

The cloud account kept showing the old name for a while, which looked like the fix hadn’t worked. It was just sync lag. After the next cycle finished, her sign-in name and email matched.

One heads-up for users: after a UPN change, Outlook and Teams usually ask them to sign in again, once.

What I took away from it

• Sign-in name and email address are different things in hybrid Microsoft 365, even when they look alike.
• Make UPNs match primary email addresses. It prevents exactly this confusion.
• Fix synced accounts at the source (on-premises AD), not in the cloud.
• Give sync a few minutes before assuming a change failed.

(Names and addresses in this note are made up.)