[RCU] Login with username instead of email address?

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I have dovecot configured to allow users to login with a username different from their email address.
In SQL there are two separate columns for 'username' and 'email'.
In dovecot the login query is structured like (SELECT email AS userdb_user, ... FROM table WHERE username='%u')

Someone with email 'user at example.com' can login with, for example, username 'nickname'. The problem is roundcube see's their email as 'nickname at localhost' instead of 'user at example.com' and creates a new user in the roundcube database for 'nickname'.

Is there anyway to have roundcube use the email address returned to dovecot from SQL instead of using the nickname used to login to roundcube? I could not find any settings related to this in defaults.inc.php