Office 365 – “A user with this name already exists. Use a different name”

Yesterday a friend contacted me when he was trying to recreate a mailbox in his Office 365 subscription and got confronted with the following error message: “A user with this name already exists. Use a different name.”.┬áHe already changed the account name with a “.original” postfix, but the mailbox still keeps the old mail address in the configuration. The issue is described in this support article.

As he wanted to change the mailbox type from shared to regular, he thought about renaming the old one, creating a new one, migrate the data and remove the old mailbox. Needless to say he ran in a hick-up during the creation process of the new mailbox.

PowerShell provides a quick way to discover which mailbox is using the email address. First of all, you need to open a remote PowerShell session to the Exchange environment in your Office 365 subscription. Open a PowerShell window on your pc and execute the following commands: Continue reading