“username” is not valid for UserPrincipalName – Exchange 2007

When moving mailboxes, the move may fail and produce the following error:

Error: “username” is not valid for UserPrincipalName. Valid values are: Strings that includes ‘@’, where ‘@’ cannot be the last character

Error code: -1056749110

To resolve this:

  1. Open the properties of the mailbox through Exchange Management Console

  2. Select the Account tab

  3. Select the appropriate domain from the drop down menu under “User logon name (User Principal Name)”

  4. Apply, and try the mailbox move once more.