Hi Takayuki,
Thank you for your answer.
Yes, I've created custom port type's pages.
I've tried including the form in the template and in the_content().
But in both cases, when I want to receive the post title in the mail, I just receive [_post_title].
The other part of the message are ok but not the special mail tag.
I've also tried in post or pages and it works correctly.
I don't know why.