Mine

silaro@silaro:/etc/mail$ sudo grep -Ri smarthost /etc/mail
/etc/mail/peers/provider:# used to provide ISP information (masquerade_as, smarthost, etc.)
/etc/mail/sendmail.conf:#       none:    No listener (ie, nullclient/smarthost)
/etc/mail/sendmail.conf:#       none:    No queue runner (ie, nullclient/smarthost)
/etc/mail/sendmail.conf:#       none:    No queue runner (ie, nullclient/smarthost)
/etc/mail/sendmail.cf:#O FallbackSmartHost=fall.back.host.net
/etc/mail/sendmail.cf:R$* < @ [ $+ ] : > $*             $#esmtp $@ [$2] $: $1 < @ [$2] > $3no smarthost: send
/etc/mail/sendmail.cf:R$* < @ [ $+ ] : $- : $*> $*      $#$3 $@ $4 $: $1 < @ [$2] > $5  smarthost with mailer
/etc/mail/sendmail.cf:R$* < @ [ $+ ] : $+ > $*  $#esmtp $@ $3 $: $1 < @ [$2] > $4       smarthost without mailer
/etc/mail/sendmail.cf:# pass names that still have a host to a smarthost (if defined)
/etc/mail/sendmail.cf:R$* < @ $* > $*           $: $>MailerToTriple < $S > $1 < @ $2 > $3  glue on smarthost name
/etc/mail/submit.cf:#O FallbackSmartHost=fall.back.host.net
/etc/mail/submit.cf:R$* < @ [ $+ ] : > $*               $#esmtp $@ [$2] $: $1 < @ [$2] > $3no smarthost: send
/etc/mail/submit.cf:R$* < @ [ $+ ] : $- : $*> $*        $#$3 $@ $4 $: $1 < @ [$2] > $5  smarthost with mailer
/etc/mail/submit.cf:R$* < @ [ $+ ] : $+ > $*    $#esmtp $@ $3 $: $1 < @ [$2] > $4       smarthost without mailer
/etc/mail/submit.cf:# pass names that still have a host to a smarthost (if defined)
/etc/mail/submit.cf:R$* < @ $* > $*             $: $>MailerToTriple < $S > $1 < @ $2 > $3  glue on smarthost name