I am setting up a client on Office 365. I'm doing the express migration. All the accounts have sync’d.
I started migrating a couple of accounts and the migration works. Their mailbox is created and they have all their aliases assigned to their account.
The problem is the login user name is firstname.lastname@example.org and I can’t change it.
Their primary SMTP address is email@example.com. It shows this is the primary address on-prem and when I look at their mailboxes in Exchange Admin Center online.
I need to figure out how to get this to change so their primary email address is also their login address before I can migrate any more users.