It's not that simple.

There's some good info in this post.

*Email spam prevention with lightning*
https://stacker.news/items/22625

Is there an email platform in the works like this where emails aren’t free so people will put more effort into emails and slow the spam and useless emails you see in the office environment as well 

User21000000

It could be that a solution will be a system where the sender has to put up a security bond of the amount specified by the recipient.  If the message is deemed spam by the recipient, the security bond funds goes either to the recipient or gets burned, ... whatever, as long as the sender is penalized for a message that the recipient deems to be spam.    This type of change could take a dozen years to be accepted though.

bitcoin

Bitcoin scams 

It could be that a solution will be a system where the sender has to put up a security bond of the amount specified by the recipient.  If the message is deemed spam by the recipient, the security bond funds goes either to the recipient or gets burned, ... whatever, as long as the sender is penalized for a message that the recipient deems to be spam.    This type of change could take a dozen years to be accepted though. 
   