Quite a lot of information in an e-mail’s headers can be forged, so you need to know what to look for and what to ignore when determining if mail is real or not.
Many times, it’s not possible to know conclusively, in which case you should assume it’s fake and proceed accordingly.
Refusing to click on links from unexpected messages (instead going straight to the source, like your bank, with a URL you know to be valid) is a good practice in general these days.