Add a hook to wp_mail() to track Google Analytics Event

I would use phpmailer_init (unless you’re using a plugin that overrides wp_mail):

function trigger_contact_event( $phpmailer ) {
    // See PHPMailer class for available properties & methods if you need
    // information about the email being sent.
}

add_action( 'phpmailer_init', 'trigger_contact_event' );