Qmail and emails hosted on another server

[NaSOnWeb]

Hello everybody
I have a little special config
My serveur with plesk host my website toto.com
I manage my domain by my registar interface
I host my emails @toto.Com by my registar (not on my plesk server)
my problem is
If I send an email by my plesk server with qmail
qmail think I host the domain
and qmail try to put this email on localhost
qmail don't try to analyse DNS zones to see the good MX to send the email
do you know a solution for this problem ?
and If I change to postfix server, is this problem still there ?
thanks a lot
and sorry for my bad english :'(