@toss, try this... put this code in your active theme functions.php file:

function my_custom_email_html_tags( $allowed_html ){
    if( $allowed_post_html = wp_kses_allowed_html( 'post' ) ){
        $allowed_html = $allowed_post_html;
    }
    return $allowed_html;
}
add_filter( 'wpforo_kses_allowed_html_email', 'my_custom_email_html_tags');

How to Easily Add Custom Code in WordPress (without Breaking Your Site)