Incoming Mail Spam can easily overwhelm you by flooding your mailbox and filtering manually is a tedious work. 
It is also dangerous considering that some emails may include security threats. 

If you are rocking a linux VPS or a dedicated server with cPanel / WHM installed on it there is a quick way to block most of the email spam in 2 clicks. 
It will be 100% accurate for the spammers spoofing email addresses.

The tip consists in blocking all incoming mails which doesn't have the SPF (Sender Policy Framework) configured on their mailing server, which is a simple verification step 

You can find the steps below: 

1) Login to WHM : https://yourserverIP:2087


2) Click in the WHM side bar on Exim Configuration Manager

3) Once, on the Exim Configuration panel, you would need in the basic editor view to search for the Reject SPF failure and activate it as shown in the screenshot below : 

That's it! All the spoofed emails will not land your inbox and only legitimate email addresses will go through which would solve most of your inbound spam issues.