dead letter office

noun2

1. •
   The postal facility that deals with mail that cannot be delivered.

   • There are 4201 letters lying in the Dead Letter Office, London, which contain property to the amount of $200,000. — 1847
2. •
   (figurative) A channel of communications for which the recipient neither acknowledges nor acts upon any messages sent.

   • The whole world is a Dead Letter Office. No one's listening to us. Our words vanish in the wind. — 2009