@email_admin I think it is not possible to change the user names in an easy way, because MiaB has a fix process how to handle the creation of user directories (e.g. dovecot LMTP create the user directories based on the E-Mail address inputs). Guess you would then need to manually adjust the user folders and the user DBs, so even if you use @pxl workaround proposal, there is a danger to mix things up. I had a similar issue in regards to the creation of users before MiaB Box DNS is set up fully.