If you're using a web browser, Chrome, Firefox, Internet Explorer, Opera or Edge rather than an email program you can see a lot about an emails source and its travels.

Open the email.
On the right side look for a star, a left facing arrow and  three dots aligned vertically.  Click on the the 3 dots.
In the menu that opens click on Show Original
Scroll down and look at all the information, origin, route and you can see if it was really sent to you.

If you are using Thunderbird all you have to do is click on the email, then press Ctrl + U and it will show you all the information too.