Mail Detective 1.3 MAS | macOS | 5 mb

Mail Detective tries to determine the geographical origin of email messages in your INBOX via geolocation by parsing the message headers for the sender's IP address, which makes it easier for you to check how plausible the message is. Simply drag the email from your mail program and drop it onto the app’s window - Mail Detective will tell you the country and, if this information is available, the city from which the email was sent.

Mac App Store: https://geo.itunes.apple.com/app/id869249991