{mail_nav}
{mail_nav:prev_id}

 {mail_nav.lprev}

{/mail_nav:prev_id}
{mail_nav:back}

{mail_nav.lback}

{/mail_nav:back}
{mail_nav:next_id}

{mail_nav.lnext} 

{/mail_nav:next_id}
{/mail_nav}