We all know what spam is, right? It's those annoying emails that pop up in your email inbox that you've never asked for, that you don't want, and that tend to try to sell you something shady.
The spam folder in your email client is the cesspool of the internet. This is where you find scams, shady offers, attempts at selling various drugs, fake lottery winnings and occasionally that one important email you thought you never received.
How does an email become spam?
Your email server analyzes every email it receives, trying to figure out if that email is one you actually want to receive. It uses a bunch of different metrics, some known, some unknown. The process of doing so is called a spam filter.
Depending on your email client, you might also have a spam filter running on your device, which acts a final stopgap for the few spam emails that the email server didn't manage to catch.