X-Originating-IP: [192.162.216.194]

Received: from 127.0.0.1  (EHLO smtp-out4.electric.net) (192.162.216.194)
  by mta1017.mail.ir2.yahoo.com with SMTPS; Thu, 20 Apr 2017 16:03:43 +0000
Received: from 1d1EYY-0008Hr-TS by out4b.electric.net with emc1-ok (Exim 4.87)
    (envelope-from <www-data@[our domain].com>)
    id 1d1EYY-0008Lj-Vu
    for [recepient]@yahoo.co.uk; Thu, 20 Apr 2017 09:03:42 -0700
Received: by emcmailer; Thu, 20 Apr 2017 09:03:42 -0700
Received: from [our IP] (helo=mail3.[our domain])
    by out4b.electric.net with esmtps (TLSv1.2:DHE-RSA-AES128-SHA:128)
    (Exim 4.87)
    (envelope-from <www-data@mail3.[our domain]>)
    id 1d1EYY-0008Hr-TS
    for [recipient]@yahoo.co.uk; Thu, 20 Apr 2017 09:03:42 -0700

$ /usr/sbin/exim4 -bt postmaster@gmail.com
R: domain_literal for postmaster@gmail.com
R: dnslookup_secure for postmaster@gmail.com
postmaster@gmail.com
  router = dnslookup_secure, transport = remote_smtp_secure
  host gmail-smtp-in.l.google.com      [2607:f8b0:400d:c0d::1a] MX=5
  host gmail-smtp-in.l.google.com      [209.85.232.26]          MX=5
⋮

$ /usr/sbin/exim4 -bt postmaster@gmail.com
R: smarthost for postmaster@gmail.com
postmaster@gmail.com
  router = smarthost, transport = remote_smtp_smarthost
  host einstein.home [192.168.65.24]