This is one of many protocol behaviors described in ActivityPub.

Identifier

urn:uuid:4592b2b2-9f47-4db6-a0a1-e7ba637b002e

Content

Servers MUST also exclude actors from the list which are the same as the actor of the Activity being notified about.

Origin

prefix Servers MUST de-duplicate the final recipient list.

Servers MUST also exclude actors from the list which are the same as the actor of the Activity being notified about.
 
suffix That is, actors shouldn't have their own activities delivered to themselves.

https://www.w3.org/TR/activitypub/

JSON

{
  "id": "urn:uuid:4592b2b2-9f47-4db6-a0a1-e7ba637b002e",
  "uuid": "4592b2b2-9f47-4db6-a0a1-e7ba637b002e",
  "type": "Behavior",
  "content": "Servers MUST also exclude actors from the list which are the same as the actor of the Activity being notified about.\n",
  "context": [
    "https://www.w3.org/TR/activitypub/",
    {
      "name": "7. Server to Server Interactions",
      "id": "https://www.w3.org/TR/activitypub/#server-to-server-interactions"
    },
    {
      "name": "7.1 Delivery",
      "id": "https://www.w3.org/TR/activitypub/#delivery"
    }
  ],
  "origin": {
    "source": "https://www.w3.org/TR/activitypub/",
    "section": {
      "id": "https://www.w3.org/TR/activitypub/#delivery",
      "branch": [
        7,
        1
      ]
    },
    "selector": {
      "type": "TextQuoteSelector",
      "prefix": "Servers MUST de-duplicate the final recipient list.\n",
      "exact": "Servers MUST also exclude actors from the list which are the same as the actor of the Activity being notified about.\n",
      "suffix": "That is, actors shouldn't have their own activities delivered to themselves.\n"
    }
  },
  "@context": [
    "https://www.w3.org/ns/activitystreams",
    "https://socialweb.coop/ns/testing/context.json"
  ]
}