Filter: postie_subject

This filter is called after the subject has been determined. Note that the subject can be in the email subject or the email body. You could use this filter to modify the subject before categories, post format and post type are detected.

add_filter('postie_subject', 'my_postie_subject');

function my_postie_subject($subject) {
    return '[promo] ' . $subject; // force the addition of the promo category

Action: postie_register_shortcode_pre

This action is called just before postie_post_before.

You use this action to register any Postie specific shortcodes.

function my_postie_register_shortcode_pre() {
    //register any Postie shortcodes
    add_shortcode('myshortcode', 'my_shortcode');

add_action('postie_register_shortcode_pre', 'my_postie_register_shortcode_pre');

// works like a standard shortcode
function my_shortcode($att, $content = null) {
    global $postie_post; // the current post
    return '<p>My shortcode</p>';