UPDATE 2:36 GMT:
Thanks for those in the comments (kessler27, Hoku and especially hurricanebtvs) and Jay who emailed me for pointing out that the "[no subject]" email contains the phrase: "Love you madly"
The email from Jay explains how it was solved:
Sam seems to have spent some time with his computer as two new emails have come in and two have gone out.
(edit: Thanks SpOOky for combining the email which requires scrolling into one image)