[Dovecot] [ #14832]: Capital letters in POP3 logins

[Jakob Hirsch]

support at majordomo.ru wrote:

> Can I solve this problem or it is virtually "bug" of dovecot?

No bug, just the "garbage in, garbage out" principle.
Mysql's string matches are case-insensisitive by default, so when 
dovecot asks mysql for the user information of UsEr1, it will get the
information of user1 and therefore assumes that UsEr1 is a valid login.
It's not dovecot's fault.
If you want the match case-insensitive (so UsEr1 will be rejected), add
the BINARY attribute to the userid field or change your query to '...
WHERE BINARY userid = "%u"' in password_query and user_query.

If you want to allow logins as UsEr1 (and let him access user1's mail), 
you have to change your dovecot.conf, I think. Use %h instead of %u 
there, and let user_query return the home directory with something like 
'SELECT CONCAT('/var/spool/vmail/',LOWER(userid)) AS home, ...'.