Here’s a very common scenario in Office 365.
There is an existing user, Gordon Jackson in this case, happily using Outlook and Exchange Online via Office 365. In their Outlook the mailbox has their email address (email@example.com).
Now let’s say that user leaves the business. The existing account is renamed to the new user so the Office 365 license can be re-used. To do this we login to the Office 365 portal as an administrator and select the existing user.
Then simply enter in the details of the new user. Here we have renamed Gordon Jackson to James Hill and we have changed the email address to firstname.lastname@example.org.
When complete we press the Save button at the bottom to update the details.
Back on the users workstation if we close and reopen Outlook we are prompted to enter the new credentials. Unless you elected to change the users password in the portal it will remain the same. Thus, you simply need to enter the new users login name.
With the new users logged in they can receive emails at their new address as you can see above, however the name of the mailbox is still the old user! Thus, the mailbox still reads gordon.jackson@ not james.hill@.
If you want to change that, close Outlook on the users desktop and go into Control Panel.
In Control Panel select Mail.
Now select E-mail Accounts.
You should see the Microsoft Exchange account listed but with the old users details.
Select this account and then press the Change button.
All the information here is normally set up by the Exchange autodiscover DNS records. You will again see the old users account in the User Name field.
Select the old user account name and delete it. In its place put the new users account details. in this, we change gordon.jackson@ to james.hill@.
Once you have done that press the Check Name button.
It may take a few moments for the verification process to complete but when it does successfully you should see the new users name underlined as shown above.
Press the Next button to continue.
Now press the Finish button to complete the process.
You should now find the account correctly displayed with the new user name in the Accounts Settings dialog as shown above.
and now when you launch Outlook the name of the mailbox should also show the new users details.