Taking someone’s junk mail

Is it permitted to take the advertisement brochures that are distributed in apartment buildings for free?

If these magazines are lying outside, one is permitted take just one, even if this is not his building. The reason is that the residents of the building didn’t acquire these magazines yet. Nonetheless, it is forbidden to take more than one magazine, since that would constitute stealing from the company that distributes them. If these magazines are inside mailboxes, then there are several different cases. If the mailbox is open, then taking a magazine does not constitute stealing, since this mailbox is considered to be an “unguarded courtyard” (in which the owner does not acquire objects automatically). If the mailbox is closed and the mail in the box does not protrude outside the box, then this is considered to be a “guarded courtyard”, and the mail inside the box belongs to the box’s owner. The case where the box is closed, but it’s not difficult to take the mail out is a matter of disagreement between latter commentators. Netivot HaMishpat (chapter 200) holds that any place that is surrounded by a fence, even if the fence is such that it doesn’t actually “guard” what is inside the perimeter, and it’s not difficult to take objects from the surrounded area, this is still considered to be a “guarded courtyard” (which acquires objects for its owners). On the other hand, Sepher HaMikneh (on tractate Kiddushin 26) is of the opinion that any area that is not actually guarded by a fence (even if it is surrounded by one) is not considered to be a “guarded courtyard”.   

Shulchan Oruch, section Choshen Mishpat, chapter 200