outbox

• (Received Pronunciation)
  • (noun): enPR: outʹbŏks, IPA^(key): /ˈaʊtbɒks/

  • Audio (Southern England):

    (file)

  • (verb): enPR: out-bŏksʹ, IPA^(key): /aʊtˈbɒks/

  • Audio (Southern England):

    (file)

  • Rhymes: -ɒks
• (General American)
  • (noun): enPR: outʹbäks, IPA^(key): /ˈaʊtbɑks/
  • (verb): enPR: out-bäksʹ, IPA^(key): /aʊtˈbɑks/

From out +‎ box.

English Wikipedia has an article on:

outbox

Wikipedia

outbox (plural outboxes)

1. A box holding papers to be transmitted to others, usually by mail.
   • 2013, Michael O'Shea, Blood on the Risers, page 226:

     Rabin tossed the orders in his outbox, dipped the brush back in the small bottle, and continued to apply more solvent […]

2. (computing) An electronic folder serving the same purpose, for electronic mail.

• inbox

From out- +‎ box.

outbox (third-person singular simple present outboxes, present participle outboxing, simple past and past participle outboxed)

1. (boxing, transitive) To box better than.

• box out, boxout