Custom shortcode in a post is interpreted as text in e-mail

@bigs38.

I cannot get the PHP shortcode to return anything other than NULL using your code, I used:

global $post_id;
return get_the_post_thumbnail( $post_id, 'medium' );

For me that worked on the front end of the blog and also in the emails.

It’s perfect, I have worked on your exemple to adapt it to my needs and it works very well now.

A short exemple, if someone need to add a link to a gallery on to the Featured image:

global $post_id;
$exemple = '<a href="https://www.mysite.com/galerie/'.$atts[id].'">';
$exemple .= get_the_post_thumbnail( $post_id, 'medium' );
$exemple .= '</a><test>';
return $exemple;

Thank for your help and for the Subscribe2 plugin !!!
Bigs38