There are many reasons that make you to block certain users from yours Email list , 
and it is also necessary to block those emailers who are sending you spam at regular intervals , Hackers are sending virus and harmfuls codes to hack emails account througn mails.so it is always recommended to block all those emails using Filters on Emails.
How To Block Emailers Email On Gmail
- Click Create a filter under the search box at the top of any Gmail page.Fill in the appropriate fields with the filter’s criteria, and click Next Step.
- Choose the action you’d like for these messages by checking the appropriate box. ( In this case, we suggest checking Delete it. ) Click Create Filter.
To edit or disable a filter, click Settings at the top of any Gmail page, and open the Filterstab.
How To Block Emails/Sender On Yahoo
- Yahoo Mail Classic- Follow the Options link in the top navigation bar.Select Block Addresses, Enter the email address you want to be blocked under Add Block, Select Add Block , Select Yes to set the block.
- New Yahoo Mail - Select Options > Mail Options in Yahoo! Mail , Go to the Spam category ,Type the unwanted email address under Add a blocked address , Click Add , Now click Save Changes.
