When UPS say "left at Mailbox" does that mean through the letterbox?

[BernadetteRostankowskiWolowitz]

Home all week apart from this afternoon, and coincidentally UPS have said they are now delivering an item this afternoon (should have been this morning). The tracking notification says "delivered to Mailbox"

This means through the letterbox right?

I'm panicking that they may have left the item on the doorstep (at street level). I tried to log in this morning to redirect to someone else, but it kept kicking me out of the site.