Google uses a highly sophisticated spam filtering engine. It is arguably the best in the world.
The paradigm does not rely on a personal control of spam filtering at the user level, but an intelligent algorithm. Thus, as a user, you can train Google for email that is spam or not spam.
Anything that is spam should be marked as such with the button, “Report Spam,” for the respective email. Anything that is not spam which is found in the spam folder should be marked as “Not Spam.”
This trains Google’s mail system to calibrate to what is spam and what is not spam over time. Gmail’s spam filtering is community-driven. Users help to define the spam algorithm and criteria.
Thus, there are two best practices for tuning the spam filter:
1. Mark emails as Spam or Not Spam
2. For emails that are “Not Spam” save the email address in your Contacts list
Over time, your email will be filtered correctly. You can learn more about Google’s approach by clicking here.