This is how the email part is displayed by the `WP_Comments_List::column_author()` method:

 /* This filter is documented in wp-includes/comment-template.php */
 $email = apply_filters( 'comment_email', $comment->comment_author_email, $comment );
 
 if ( ! empty( $email ) && '@' !== $email ) {
 printf( '<a href="%1$s">%2$s</a><br />', esc_url( 'mailto:' . $email ), esc_html( $email ) );
 }

so you're most likely looking for the `comment_email` filter.

**Update:**

Here's a hack to add a *subject* and *body* to the `mailto` part:

 add_filter( 'comment_email', function( $email )
 {
 // Target the edit-comments.php screen
 	if( did_action( 'load-edit-comments.php' ) )
 		add_filter( 'clean_url', 'wpse_258903_append_subject_and_body' );		
 
 	return $email;
 } );
 
 function wpse_258903_append_subject_and_body( $url )
 {
 // Only run once
		remove_filter( current_filter(), __FUNCTION__ );

 // Adjust to your needs:
 $args = [ 'subject' => 'hello', 'body' => 'world' ];

 // Only append to a mailto url
		if( 'mailto' === wp_parse_url($url, PHP_URL_SCHEME ) )
			$url .= '?' . buld_query( $args );
 
 	return $url;
 }

Note that this targets the first `esc_url()` after each time the `comment_email` filter is applied, on the `edit-comments.php` page.

We added a *mailto* check to make sure it's for the email part.