Why do I need to change the domain name from onmicrosoft.com, and what are the steps to do this?
When performing a tenant to tenant Office 365 migration while keeping the same domain name, and using DeploymentPro (Legacy) to automate the configuration of your Outlook profiles, there is an additional step required from the normal procedures that are covered in the video in KB004775.
The reason for this is that tenant to tenant migrations require that you migrate using the tenantname.onmicrosoft.com addresses on both the Source and the Destination. This is because the process requires that you remove the Source vanity domain name (but leave the source.onmicrosoft.com domain name intact) before you verify the vanity domain name on your Destination. A Pre-Stage Migration pass is also run against the destination.onmicrosoft.com domain name before the vanity domain name is verified, hence the reason for using the destination.onmicrosoft.com domain name. The step-by-step migration guide can be found in KB005005.
When creating the profile, using DeploymentPro (Legacy), create the profile against the vanity domain name, rather than the destination.onmicrosoft.com domain name.
You can copy the entire Office 365 email column into a spreadsheet, and then run a search and replace to search for the .onmicrosoft.com domain name and replace it with the vanity domain name. Once completed, you can then copy this column into your clipboard, and paste this column back into the spreadsheet page of MigrationWiz, to override the existing column with the onmicrosoft.com entries. Important: Make sure that the usernames line up correctly for Source and Destination.
Once completed, click on the Done button to save this list and return to your project.