There are lots of email you received is not related to your requirements i.e. most annoying things about the internet. And it's just email spam that's fill up your inbox. You get emails from every website where you are registered. And there are many spammers who got your email id and send marketing emails on daily basis. You can not check each of spam emails that is not relevant to you. Now, Gmail makes it easy to block emails from addresses you're not interested in.
How to Block Unwanted Emails in Gmail
How to Unblock Emails in Gmail
If you accidentally block the wrong person's, don't worry, the situation is easy to rectify:
Hope this helps someone who doesn't want the spam emails...
