If anyone knows of a solid, regular collection, please leave a link below. I'd like to link it on my wheelbarrow blog. I would have called my blog wheelbarrow.blogspot, but someone already has that; also wheelbarrows... Bummer. Someone has mailbox.blogspot, too, but there's only one single photo from May 2012.
I found these smaller-than-a-blog collections:
23 Pleasant Mailbox PicturesI take photos of my own mailbox sometimes. I wish I had more, of all my mailboxes ever (though there haven't been that many). Take a picture of YOUR mailbox!!
17 Pictures of Old Rustic Mailboxes
Here in ‘Merica, we love our mailboxes (34 Photos)