problem with mail function

[deseosx1]

i have a site with you... http://deseos.x10.mx and i am developing the site with PHP,

and i use the mail function with several actions (like the registration), i send a confirmation mail....
Every was fine, until yesterday.... the mail didn't go out...

with several tests, i found that a reference with a slash ("/") stop the sending...

This is the code:
$email_message = "Gracias por Registrarse con nosotros ".$username."\n\n Aqui esta su Liga de activación.\n\n Si la liga no funciona Copie el siguiente renglon en su navegador.\n\n http://deseos.x10.mx/activate.php?code=".$code;
$cuerpomsg ='
Gracias por Registrarse con nosotros '.$username.'
Aqui esta su Liga de activación.
En su navegador pegue esta línea con el cambio requerido:
deseos.x10.mx(diagonal)activate.php?code='.$code.'
Cambiar (diagonal) por una "/" (sin comillas)
Esto es para comprobar que es humano y no un robot (Disculpa las molestias) ';

mail($emailo,$email_subject,$cuerpomsg,$cab); // this is working because don't have the slash.... but
mail($emailo,$email_subject,$email_message,"From: noreply@deseos.x10.mx"); // this is not working because the slash in the URL

can sombody tellme hay can i solve this problem?
i need to send the URL in the mail

Thank you for your ASAP answer...
BEST REGARDS

Juan Cortés
e-mail: jpopulos1@hotmail.com