Postmen already have them if you've paid for postage online and requested collection. Post boxes in the UK are not like US mailboxes, these are communal and fo

Postmen already have them if you've paid for postage online and requested collection. Post boxes in the UK are not like US mailboxes, these are communal and for outgoing mail only. Postmen (typically, exception per first paragraph) only being your incoming mail, and it goes in a letterbox in or near your door, almost always depositing the mail inside your house; there's no way for them to reach outgoing mail you've left there.