I use this short code to send a simple confirmation e-mail to a user who has forgotten their password and has click "generate new password"
mail($email,'password recovery','Your temporary password is '.$generatedpassword ,'From: do_not_reply@do_not_reply.com');
It works just fine on my private server but when I pushed my PHP code to BlueMix the users never get that e-mail.
As I mentioned above the code works just fine on my server, which leads me to believe that this is a BlueMix specific issue.