[georgemcbay]

In the USA, most commercial mass advertising mail is in large printed flyer form, not enclosed in any kind of external envelope.

Kinda like this:

http://thumbs.dreamstime.com/z/sale-advertising-papers-15592...

The advertisers pay bulk rates to USPS to stuff all this crap directly in our mailboxes.

There are some exceptions which arrive in envelopes, mostly to trick you into thinking it isn't just spam mail like the rest of the crap.

[tdkl]

Yep, same here. We do have an option to place a special sticker on the mailbox, which indicates to the postal worker that he doesn't put that kind of bulk commercial material inside.