Sorry, but your problem does not imply a bug in PHP itself.  For a
list of more appropriate places to ask for help using PHP, please
visit http://www.php.net/support.php as this bug system is not the
appropriate forum for asking support questions. 

Thank you for your interest in PHP.

Please post scripting questions to php-general@lists.php.net

As to your specific problem, it is most likely cause by one or more newlines in your subject variable "$sujet" or in your $envelope.

Some mail clients will attempt to accomodate such missends, others will work despite them (quasi-incorrect behavior mind you), and others will be strict about it.

A good debugging trick you can use to find the location of the spurrious newline in Outlook is to right click on the message, select "Options", and view the header contents in the window which pops up.