I have been working with a customer in a case with a migration of mailboxes from one Office 365 User to another. You might have done this on on-premises Exchange...
Blog
Use DHCP to detect UEFI or Legacy BIOS system and PXE boot to SCCM
I’ve been working on a customer setup where I needed to be able to support legacy bios devices and UEFI devices. We didn’t have access to the customer network equipment...