Though it is not possible to prevent the DMA from setting the UPN on Office 365, Mapping Rules can be used to set the UPN in a preferred format. In Migration Manager for Active Directory (Office 365), you can create a Mapping Rule at either the Domain Pair level, or on individual Collections.
If the Source AD accounts have an attribute that contains the value that is preferred for the Office 365 UPN, a Mapping Rule can be created to Set the UPN to match that Source attribute.
For example, if the Source AD account has a 'mail' attribute of first.last@<domain.com> and this is the preferred UPN in Target, then the following Mapping Rule can be created:
- Click on the Mapping tab.
- Click on Add Mapping Rule.. on the right Actions bar.
- In the Add Attribute Mapping dialog box, select the following:
- Target class: User
- Target attribute: UserPrincipalName
- Select the rule to apply: Copy From
- Source class: User
- Source attribute: mail
Note: Any single-valued String attribute can be used in Source. If there is not a currently populated attribute in Source, Professional Services can be engaged to create a script to populate an attribute with the preferred UPN value on Source accounts. Once an attribute exists in Source that contains the preferred UPN for Office 365, select that attribute in the Mapping Rule example above under Source attribute: