postfix and local transport

[chris734]

Hello, my problem is : (sorry my bad english)

IspCP use for my hosting.
My mails are hosted by a postfix but on another server.
To receive e-mails and sent with an email client, I have no problem.

if I send a mail white a form contact@toto.fr, domain hosted toto.fr. The mail does not exist on the hosting server and therefore I receive a message from 'Mail Delivery System
to webmaster unknown user: contact@toto.fr '

it Is normal, only [b] I'd like disable local transport [/ b] postfix to force the mail to go out on my extern mail server.

I tried several conf, but the mail don't send or it's undelivry.

My postfix version:
mail_version = 2.5.5