Q:

Send notification to the admin when new custom post is submitted

I have a cpt called "auto" and i make a frontend form to create new post with "pending" status. 
After the post submission i would receive an email with a notification of the new post. 
function newpost_notify() {

  $mailadmin = 'xxx@domain.com';
  $subject = 'Subject';
  $headers  = 'MIME-Version: 1.0' . " \r\n";
  $headers .= 'Content-type: text/html; charset=UTF-8' . " \r\n";    
  $headers .= 'From: xxx <noreply@domain.com>' . " \r\n";
  $message = 'There\'s a new post.'; 

  wp_mail( $mailadmin, $subject, $message, $headers );
}

add_action( 'publish_post', 'newpost_notify', 10, 2 );

This is my code..but i didn't receive any email. 
I would know if there's a difference between a "new post" and a "publish post", because i read something about the post status transition. 
Thank you

A:

EDIT - SOLUTION
I got the solution using status 'new_to_pending' and adding the $auto object.  
function newpost_notify( $auto ) {

  $mailadmin = 'xxx@domain.com';
  $subject = 'Subject';
  $headers  = 'MIME-Version: 1.0' . " \r\n";
  $headers .= 'Content-type: text/html; charset=UTF-8' . " \r\n";    
  $headers .= 'From: xxx <noreply@domain.com>' . " \r\n";
  $message = 'There\'s a new post.'; 

  wp_mail( $mailadmin, $subject, $message, $headers );
}

add_action( 'new_to_pending', 'newpost_notify', 10, 2 );

thanks to the constructive comments of @Rarst & @flomei

