Did you know that it is illegal for the public to put flyers in US mailboxes? You could be fined for every flyer you insert into a mailbox. It is also illegal to affix the flyer to the box or the flag in any way.
Use the newspaper box if there is one (below the mailbox) ior better yet hand deliver the flyer to the door. When you put the flyer directly into the homeowner’s hands they have a better chance of remembering you and the story of your missing dog. You aren’t just trying to find out who has seen your dog, you are trying to alert the people who MAY see your dog tomorrow. Make it easy for them to contact you!
Not everyone is on Facebook or social media. Hand-delivered flyers are still the Number One way that lost dogs are found.