Seems unlikely if it was an email from answering a Craigslist ad. Craigslist sends an email with your reply to an ad everytime you reply to an ad for reference. It is doubtful unless it was a "fake" Craiglist email sending a "fake" email.
The sent email had an craigslist created email and the respond my ex gave. I clicked on the link and it had already expired but apparently it was real. I really just wanted to know if it was possible that spam can be found in the sent box of an email. I am not that tech savy.