To add UPN suffixes

  1. Open Active Directory Domains and Trusts. To open Active Directory Domains and Trusts, click Start , click Administrative Tools , and then click Active Directory Domains and Trusts .
  2. In the console tree, right-click Active Directory Domains and Trusts , and then click Properties .
  3. On the UPN Suffixes tab, type an alternative UPN suffix for the forest, and then click Add .
  4. Repeat step 3 to add additional alternative UPN suffixes.

Note: You must be a member of the Domain Admins group or Enterprise Admins group

Change the UPN suffix for existing users

  1. On the server that Active Directory Domain Services (AD DS) runs on, in the Server Manager choose Tools > Active Directory Active Directory Users and Computers.
  2. Select a user, right-click, and then choose Properties.
  3. On the Account tab, in the UPN suffix drop-down list, choose the new UPN suffix, and then choose OK.

Run the following Windows PowerShell commands to update all contoso.local suffixes to contoso.com:

$LocalUsers = Get-ADUser -Filter {UserPrincipalName -like '*contoso.local'} -Properties userPrincipalName -ResultSetSize $null
$LocalUsers | foreach {$newUpn = $_.UserPrincipalName.Replace("contoso.local","contoso.com"); $_ | Set-ADUser -UserPrincipalName $newUpn}

TechNet | Office