All authentications are done by an imap authentication....so you can create an user in egroupware but you can't connect to that user in egroupware.
It is the same if you want to change the user password...you have to do it trought the server-manager or the user-manager...no changes are allowed in egroupware.
If you want to create a new user in egroupware, please do it in the server-manager first and after connect you in egroupware