Change All UPNs in a Domain

I needed to update all UPNs in a domain today. It was pretty quick to figure out, but here is one line to take care of it for you.

Get-ADUser -Filter * | ForEach-Object { Set-ADUser $_ -UserPrincipalName ($_.UserPrincipalName).Replace("OldDomain","NewDomain")}

Remember to make the pattern in the OldDomain unique enough that you don't accidentally change things you don't intend to. For example, if you are changing from a .local domain in the UPN to a .com, make sure that you replace ".local" and not "local" on the off chance one of the user IDs includes "local" in the name.

If there are any user accounts without a UPN, then an error is generated for those accounts. My domain had 4 accounts without a UPN:

• krbtgt - default account used for kerberos
• IWAM_ServerName - Old IIS account from Windows 2003
• IUSR_ServerName - Old IIS account from Windows 2003
• support_XXXXXXX - Used by Help and Support service