How to override the mail notification entirely

If the built-in notification system doesn’t fit — e.g. you want to send via a transactional email service, attach generated PDFs, conditionally pick between templates, or run async — bypass it entirely:

Remove every notification from Form Settings → Notifications.
Send your own email from af/form/submission using wp_mail() (or the SDK of whichever email service you use).

add_action( 'af/form/submission', function ( $form, $fields, $args ) {

    // Only run for the target form.
    if ( $form['key'] !== 'YOUR_FORM_KEY_HERE' ) {
        return;
    }

    $to      = af_get_field( 'email' );
    $subject = 'Thanks for your submission';
    $body    = 'Custom message body here…';
    $headers = [ 'Content-Type: text/html; charset=UTF-8' ];

    wp_mail( $to, $subject, $body, $headers );

}, 10, 3 );

This gives you full control — and full responsibility. You’re no longer benefiting from Advanced Forms’ built-in merge-tag resolution or email templating, so build those into your handler as needed.

When to use the existing filters instead

If you only need to tweak one or two aspects of the built-in notification, the dedicated filters are usually less work:

af/form/email/recipient — change who receives the email.
af/form/email/headers — add CC/BCC/Reply-To.
af/form/email/styles — modify the email CSS.

Reach for the “send your own” pattern only when those filters aren’t enough.