Force mailbox usernames to lower case?
When this field is set to Yes (as it is by default), all mail / FTP
users will have their usernames forced to lower case, regardless of what
case they are created in. If you want to prevent this behaviour, select
No to have mailboxes created with the exact case entered. Be aware
that for logging into Usermin and any POP3, IMAP or FTP server, the correct
case must be used.
Because most mail servers cannot handle delivery to users with non-lowercase
names, this option should always be left set to Yes unless you are
creating accounts for FTP, DAV or SVN use.