[Environment]
SDS IAM & EMM devices managed via Active Directory Group Policy Objects (GPO)
Exchange ActiveSync (EAS) mailbox

[Summary]
You are looking to migrate users that are currently managed using Group Policy Objects to a new email server. 

[Resolution]
If users are migrated as a single group:

1. Migrate all the user mailboxes to the new email server
2. Remove the existing EAS profile for mobile devices in the current GPO
3. Create a new profile pointing to the new server in the current GPO
4. Allow some time for the policy changes to get applied to the device.

If smaller groups are being migrated, use the following steps to allow devices associated with the user mail boxes to use your current Exchange profile: 

1. Create a new Organizational Unit (OU) containe
2. Duplicate the existing GPO and apply it to the new OU.
3. In the new GPO, remove the existing EAS profile .
4. In the new GPO, create a new profile pointing to the new server
5. Migrate the user mailbox to the new email server.
6. Move the devices of the migrated users from the old OU container into the new container. 
7. Allow some time for the policy changes to get applied to the device.

NOTE — There are multiple policy options to configure Exchange ActiveSync profiles. You may need to configure iOS, Touchdown (Android), and Samsung Standard devices separately to ensure delivery to all devices.