Hi Julian,
thanks for your quick answer!
This is the code I tried (of course i changed ‘[email protected]’ to the sender address)
add_filter( 'haet_mail_use_template', 'customize_template_usage', 10, 2 );
function customize_template_usage( $use_template, $mail ){
if( $mail['from'] == '[email protected]' )
return false;
return $use_template;
}