Can I put business cards in mailboxes?

It is not effective, and it is not legal. In the United States, mailboxes are federal property reserved for stamped mail, so slipping a card inside can draw fines and almost always ends with the card in the trash. The better use of your budget is a distribution method that actually reaches people.

• Direct mail: a USPS-compliant postcard or mailer is trackable and lawful.
• In-person handoffs: networking events, trade shows, and counter drops build real recall.
• Community placement: bulletin boards, local shops, and door hangers on the door, not in the box.

Spend your effort on channels that convert and keep your reputation intact rather than risking a penalty for a card no one keeps.