[Dovecot] POP3 protection

[Jos Chrispijn]

I have some users that I will not allow to use POP3 thru my system, but 
force them to use webmail.
Would it be possible to put an extra option in dovecot.conf to force this:

# -----------------------------------------------------------------
#  Logon processes
#  user = <username>,<password>
# -----------------------------------------------------------------

user = johndoe,another_secret_password
user = mike,trouble_in_paradise

If unix user johndoe logs on, he cannot fetch mail thru POP3 for he has 
a differect password from his logon password.

thanx for listening,
Jos