Currently emails sent using [[Special:EmailUser]] are not easily identifiable to the receiver as there is no clue that the email has been sent using MediaWiki without examining full email headers. In order to improve this, emails should have text like the following appended to them: "Email sent using MediaWiki's email feature. Site:example.website.com / Sent by User:Example"
I am aware the username of the sender is in the "from" field but this is insufficient as there is no way to know the e-mail came from MediaWiki so the name in the from field could mean anything. In addition, this would simplify email blocking of spammers using [[Special:EmailUser]] to distribute their spam.