diff --git a/src/activitypub/helpers.js b/src/activitypub/helpers.js
index 9588353623..b54366fa4c 100644
--- a/src/activitypub/helpers.js
+++ b/src/activitypub/helpers.js
@@ -154,6 +154,9 @@ Helpers.resolveLocalId = async (input) => {
 					const uid = await user.getUidByUserslug(value);
 					return { type: 'user', id: uid, ...activityData };
 				}
+
+				case 'message':
+					return { type: 'message', id: value, ...activityData };
 			}
 
 			return { type: null, id: null, ...activityData };
diff --git a/src/activitypub/inbox.js b/src/activitypub/inbox.js
index 9b38242bc9..06a9d09111 100644
--- a/src/activitypub/inbox.js
+++ b/src/activitypub/inbox.js
@@ -62,9 +62,9 @@ async function announce(id, activity) {
 inbox.create = async (req) => {
 	const { object } = req.body;
 
-	// Temporary, reject non-public notes.
+	// Alternative logic for non-public objects
 	if (![...object.to, ...object.cc].includes(activitypub._constants.publicAddress)) {
-		throw new Error('[[error:activitypub.not-implemented]]');
+		return await activitypub.notes.assertPrivate(object);
 	}
 
 	const asserted = await activitypub.notes.assert(0, object);
diff --git a/src/activitypub/notes.js b/src/activitypub/notes.js
index cf80588ad1..cb1468b1be 100644
--- a/src/activitypub/notes.js
+++ b/src/activitypub/notes.js
@@ -8,6 +8,7 @@ const batch = require('../batch');
 const meta = require('../meta');
 const privileges = require('../privileges');
 const categories = require('../categories');
+const messaging = require('../messaging');
 const user = require('../user');
 const topics = require('../topics');
 const posts = require('../posts');
@@ -190,6 +191,79 @@ Notes.assert = async (uid, input, options = { skipChecks: false }) => {
 	return { tid, count };
 };
 
+Notes.assertPrivate = async (object) => {
+	// Given an object, adds it to an existing chat or creates a new chat otherwise
+	// todo: context stuff
+
+	const recipients = new Set([...object.to, ...object.cc]);
+
+	// Remove follower urls
+	const isFollowerUrl = await db.isObjectFields('followersUrl:uid', Array.from(recipients));
+	Array.from(recipients).forEach((id, idx) => {
+		if (isFollowerUrl[idx]) {
+			recipients.delete(id);
+		}
+	});
+
+	const localUids = [];
+	const recipientsResolved = new Set([...recipients]);
+	await Promise.all(Array.from(recipients).map(async (value) => {
+		const { type, id } = await activitypub.helpers.resolveLocalId(value);
+		if (type === 'user') {
+			localUids.push(id);
+			recipientsResolved.delete(value);
+			recipientsResolved.add(parseInt(id, 10));
+		}
+	}));
+
+	// Locate the roomId based on `inReplyTo`
+	let roomId;
+	const resolved = await activitypub.helpers.resolveLocalId(object.inReplyTo);
+	let toMid = resolved.type === 'message' && resolved.id;
+	if (object.inReplyTo && await messaging.messageExists(toMid || object.inReplyTo)) {
+		roomId = await messaging.getMessageField(toMid || object.inReplyTo, 'roomId');
+	}
+
+	// Compare room members with object recipients; if someone in-room is omitted, start new chat
+	if (roomId) {
+		const participants = await messaging.getUsersInRoom(roomId, 0, -1);
+		const omitted = participants.filter((user) => {
+			let { uid } = user;
+			uid = utils.isNumber(uid) ? `${nconf.get('url')}/uid/${uid}` : uid;
+			return !recipients.has(uid) && uid !== object.attributedTo;
+		});
+		if (omitted.length) {
+			toMid = undefined; // message creation logic fails if toMid is not in room
+			roomId = null;
+		}
+	}
+
+	let timestamp;
+	try {
+		timestamp = new Date(object.published).getTime() || Date.now();
+	} catch (e) {
+		timestamp = Date.now();
+	}
+
+	if (!roomId) {
+		roomId = await messaging.newRoom(object.attributedTo, { uids: [...recipientsResolved] });
+		timestamp = Date.now(); // otherwise message can't be seen in room as it pre-dates participants joining
+	}
+
+	// Add message to room
+	await messaging.sendMessage({
+		mid: object.id,
+		uid: object.attributedTo,
+		roomId: roomId,
+		content: object.content,
+		toMid: toMid,
+		timestamp,
+		// ip: caller.ip,
+	});
+
+	return { roomId };
+};
+
 async function assertRelation(post) {
 	/**
 	 * Given a mocked post object, ensures that it is related to some other object in database
diff --git a/src/messaging/create.js b/src/messaging/create.js
index 2d7063a0bc..e6b7713be1 100644
--- a/src/messaging/create.js
+++ b/src/messaging/create.js
@@ -50,7 +50,7 @@ module.exports = function (Messaging) {
 				throw new Error('[[error:no-privileges]]');
 			}
 		}
-		const mid = await db.incrObjectField('global', 'nextMid');
+		const mid = data.mid || await db.incrObjectField('global', 'nextMid');
 		const timestamp = data.timestamp || Date.now();
 		let message = {
 			mid: mid,
diff --git a/src/messaging/data.js b/src/messaging/data.js
index 20568cc3f7..9cbe5d2a01 100644
--- a/src/messaging/data.js
+++ b/src/messaging/data.js
@@ -5,6 +5,7 @@ const validator = require('validator');
 
 const db = require('../database');
 const user = require('../user');
+const posts = require('../posts');
 const utils = require('../utils');
 const plugins = require('../plugins');
 
@@ -185,6 +186,8 @@ module.exports = function (Messaging) {
 	async function parseMessage(message, uid, roomId, isNew) {
 		if (message.system) {
 			return validator.escape(String(message.content));
+		} else if (!utils.isNumber(message.mid)) {
+			return posts.sanitize(message.content);
 		}
 
 		return await Messaging.parse(message.content, message.fromuid, uid, roomId, isNew);