Wikipedia:Notability (mailboxes)
For the purposes of this guideline, a mailbox (also known as a letter box) is defined as a receptacle for receiving incoming mail at a private residence or business. A mailbox-related article (MRA) is defined as an article related to mailboxes. A non-mailbox-related article (NMRA) is defined variously as either an article not related to mailboxes or an article related to something that is not mailboxes.
This guideline is independent from the other subject-specific notability guidelines, such as WP:NMAIL, WP:NPOBOX, WP:NPOSTOFFICE, etc., and is explicitly listed as an alternative to the general notability guideline. It is possible for a mailbox not to be notable under the provisions of this guideline but to be notable in some other way under the general notability guideline or one of the other subject-specific notability guidelines. Conversely, failure to meet either the general notability guideline or other subject-specific notability guidelines is irrelevant if a mailbox is notable under this guideline.