Скачать или смотреть How to Add UPN Suffixes and update your users

Synchronized with user principal names (UPN) for Office 365 synchronization on the active directory.
If you are currently using a domain name.local domain for user accounts in Active Directory, it is recommended that you use them as a verified domain ([email protected]) for proper synchronization with your Office 365 domain. This video is described in detail on step by step. You can define all users on Active Directory via powershell.
Powershell command
$ LocalUsers = Get-ADUser -Filter {UserPrincipalName -like '* company.local'} -Properties userPrincipalName -ResultSetSize $ null
$ LocalUsers | foreach {$ newUpn = $ _. UserPrincipalName.Replace ("company.local", "company.com"); $ _ | Set-ADUser -UserPrincipalName $ newUpn}