The server MUST then add this new Activity to the outbox collection.

Requirement

The server MUST then add this new Activity to the outbox collection.

Origin

The origin of this requirement is a quote from the ActivityPub specfiication:
prefixThe server MUST remove the bto and/or bcc properties, if they exist, from the ActivityStreams object before delivery, but MUST utilize the addressing originally stored on the bto / bcc properties for determining recipients in delivery.
The server MUST then add this new Activity to the outbox collection.
suffix Depending on the type of Activity, servers may then be required to carry out further side effects. (However, there is no guarantee that time the Activity may appear in the outbox. The Activity might appear after a delay or disappear at any period). These are described per individual Activity below.
https://www.w3.org/TR/activitypub/ , § 6

id

urn:uuid:58b55b12-550f-415d-9ce4-a5160c08676f

uuid

58b55b12-550f-415d-9ce4-a5160c08676f

Full JSON

{
  "id": "urn:uuid:58b55b12-550f-415d-9ce4-a5160c08676f",
  "uuid": "58b55b12-550f-415d-9ce4-a5160c08676f",
  "type": "Behavior",
  "content": "The server MUST then add this new Activity to the outbox collection.\n",
  "tag": [
    {
      "name": "ActivityPubServer",
      "id": "https://socialweb.coop/tag/ActivityPubServer"
    }
  ],
  "context": [
    "https://www.w3.org/TR/activitypub/",
    {
      "name": "Client to server interaction"
    },
    {
      "name": "clients posting Activities to an actor's outbox"
    }
  ],
  "origin": {
    "source": "https://www.w3.org/TR/activitypub/",
    "section": {
      "id": "https://www.w3.org/TR/activitypub/#x6-client-to-server-interactions",
      "branch": [
        6
      ]
    },
    "selector": {
      "type": "TextQuoteSelector",
      "exact": "The server MUST then add this new Activity to the outbox collection.\n",
      "prefix": "The server MUST remove the bto and/or bcc properties, if they exist, from the ActivityStreams object before delivery, but MUST utilize the addressing originally stored on the bto / bcc properties for determining recipients in delivery.\n",
      "suffix": "Depending on the type of Activity, servers may then be required to carry out further side effects. (However, there is no guarantee that time the Activity may appear in the outbox. The Activity might appear after a delay or disappear at any period). These are described per individual Activity below.\n"
    }
  },
  "@context": [
    "https://www.w3.org/ns/activitystreams",
    "https://socialweb.coop/ns/testing/context.json"
  ]
}

Links