These settings give you more control on the way the login name is send to the authentication server once they have been entered by the user. Think of these as “login rewriters”. This may be usefull when user must give their domain name to Mailcleaner (for multi-domain installation for exemple), but must be authentified only with their short login name to the authentication server.

only the local part of the username is passed to the authentication server. For exemple, if the user type its mail address as its mailcleaner username, then only the part before the @ sign will be sent. E.g. for myuser@mydomain.com, then myuser will be sent to the authentication server configured for the domain mydomain.com.

this one will “build” the login name based on the local part and the domain. joining them with an ”@” sign. This may be usefull if you want your user to log in only with their shortname, but the full address is needed for authentication.

this is the same as username@domain, but instead of a ”@” sign, a ”%” sign is used. Some IMAP server may need this kind of schema for correct authentication.