Decide on the target audience of the project?

Question

Startups

The other day I left a note on Habré about the Attention Auction startup , which allows you to solve the problem of a large number of incoming letters (messages), losing the right ones, wasting time parsing mail and other things.
The main idea is that the sender pays for the first cold contact with a money back guarantee if the recipient does not open the letter. The higher the price of the contact, the higher the message is in the Inbox.
For Runet, I want to decide on possible narrow niches. Based on this, we formulated the requirements for the target groups.
Please help complete the list.
Recipient Needs:

• limit the flow of incoming
  
• receive only important messages
  
• not to lose the necessary messages in the flow of letters
  
• small income (not the main thing, of course)
  

Needs and capabilities of senders:

• get the right contact
  
• ability to pay for it
  
• convey your idea to a specific recipient
  

For both groups, the Internet should be "home" so that they know how to use online payment and that the volume of the audience and recipients and senders is large enough.
Offhand it turned out like this:

• Startups - investors
  
• Musicians - Producers
  
• Writers - publishers
  
• Developers (Software) - Publishers
  

What else is possible? We really appreciate the community's help.

Answer 1

a small criticism: don't you think that everything will come down to the fact that there will be useless letters in the inbox, but with high pay. because the price is not an indicator of utility. and from this it follows that people will not bother with this thing, since the issue of money is probably less important to them than the issue of free time. maybe I'm seeing it all wrong...