Need to change a email domain to another domainname on users

Computermusen Hi,

See my answers below your questions.

1. I know that I can add a new domain to become the primary adress on the single accounts, but what about their mailboxes, dop they all get a new username and password, for logging in?
   Yes, their new adress will be ttheir primary account password will not change
2. How about the emailsender in Outlook, will that change to the new address as well, when I change the primary address on O365 admin?
   After changing, the old adress will be an alias. So they can be reached on both mailadresses. Sending email will be from the new primary account.
3. Can I change the login(username and password to the new emailadress)
   Yes, password isn't nesscary
4. Can they just use the same ost-file(folders and emails), on their accounts, or should it be synced all over again with the new account?
   Nothin wil change
5. What about Onedrive? Should the connection be changed also, and should they all sync from scratch?
   This will be done by Microsoft no action for the user.