The company would be in a unique position to know what catalogs, fliers and brands a customer likes or marks as junk, and could charge companies that wanted to reach specific demographics.

The companies currently filling up mailboxes with fliers have already been experimenting with online alternatives. If Outbox attracts enough customers and its ads are effective, it could become an alternative to sending ads through the U.S. Mail.

"As time changes the marketers evolve," said Jerry Cerasale, a vice president at the Direct Marketing Association. "The more precise they can be means less waste, less money spent on advertising, and more response."

Outbox's Davis also believes that once his company has saturated an area, it will be in a great position to handle same-day deliveries for e-commerce companies like Amazon. Eventually Outbox will also try tiered pricing for work addresses, and extra features such as forwarding individual pieces of mail to other addresses, he said

For now it's focused on polishing its service and logistics. The company has big-name backers like venture capitalist Peter Thiel and is planning on closing a "sizable" second round of funding in April. After San Francisco is fully staffed with unpostmen, Outbox plans to bring its service to New York, Boston, Chicago, Los Angeles and Washington.

Davis isn't worrying yet about competitors. "No one is crazy enough to do what we're doing," he said.