We as a team are currently migrating from Slack to Mattermost and as we did that there were some occurrences of people which did misspell their emails which lead to dead user accounts as they quickly created a new account with the right email.
As I am not the general administrator of the server it is quite intensive to get those bad user accounts removed.
It would not be that big of a deal if those users existed in the background but can not be referenced in chats or assigned to teams.
But as they are “visible” from the beginning it could lead to confusion as the new accounts have similar usernames and therefore someone could tag the wrong account or add them to a new team/channel.
Therefore, I would propose to make the user invisible to all the other users until they have verified their email.