Laundry was for 50 years often mailed. Until the 1960s, many US college students mailed dirty clothes home for moms to wash and mail back (often including food), using reusable boxes and USPS parcel post. Modern washing machines that made washing clothes locally easier ended laundry mail.
Mailing an entire building has been illegal in the U.S. since 1916 when a man mailed a 40,000 ton brick house across Utah to avoid high freight rates.
In 1916 a Salt Lake City company figured out the cheapest way to send 40 tons of bricks to Vernal Utah was to wrap each individually and send parcel post. Regulations were quickly changed to address this issue.
During WWII the US tricked the German postal service into inadvertently delivering anti-Nazi propaganda to German citizens through mail in the form of stamps.
After parcel post service was introduced in 1913, at least two children were sent by the service. With stamps attached to their clothing, the children rode with railway and city carriers to their destination. The Postmaster General quickly issued a regulation forbidding the sending of children in the mail after hearing of those examples.