Kind of. There are specs and there are blog posts and there are also existing implementations to review - but there isn’t a one size fits all solution, its more of a concept.

NIP-65: https://github.com/nostr-protocol/nips/blob/master/65.md
Mike Dillger’s post: https://mikedilger.com/gossip-model/
Hodlbod’s post: https://njump.me/naddr1qvzqqqr4gupzp978pfzrv6n9xhq5tvenl9e74pklmskh4xw6vxxyp3j8qkke3cezqq2nskt2w9vx6dznfdvj64rpw4mk5nmxf3v9xsd0gdy 

 Thank you very much for this  

 very few clients have so far implemented OUTBOX right? 

 That’s correct