diff --git a/lib/utils/conversion-utils.js b/lib/utils/conversion-utils.js
--- a/lib/utils/conversion-utils.js
+++ b/lib/utils/conversion-utils.js
@@ -5,7 +5,7 @@
 import type { TInterface, TType } from 'tcomb';
 
 import { convertIDToNewSchema } from './migration-utils.js';
-import { assertWithValidator, tID } from './validation-utils.js';
+import { assertWithValidator, tID, tUserID } from './validation-utils.js';
 import {
   getPendingThreadID,
   parsePendingThreadID,
@@ -57,6 +57,21 @@
   return convertObject(outputValidator, data, [tID], conversionFunction);
 }
 
+function extractUserIDsFromPayload<T>(
+  outputValidator: TType<T>,
+  data: T,
+): $ReadOnlyArray<string> {
+  const result = new Set<string>();
+  const conversionFunction = (id: string) => {
+    result.add(id);
+    return id;
+  };
+
+  convertObject(outputValidator, data, [tUserID], conversionFunction);
+
+  return [...result];
+}
+
 function convertObject<T, I>(
   validator: TType<I>,
   input: I,
@@ -141,5 +156,6 @@
 export {
   convertClientIDsToServerIDs,
   convertServerIDsToClientIDs,
+  extractUserIDsFromPayload,
   convertObject,
 };
diff --git a/lib/utils/conversion-utils.test.js b/lib/utils/conversion-utils.test.js
--- a/lib/utils/conversion-utils.test.js
+++ b/lib/utils/conversion-utils.test.js
@@ -4,10 +4,12 @@
 import t from 'tcomb';
 
 import {
+  extractUserIDsFromPayload,
   convertServerIDsToClientIDs,
   convertClientIDsToServerIDs,
 } from './conversion-utils.js';
 import { tShape, tID, idSchemaRegex } from './validation-utils.js';
+import { fetchMessageInfosResponseValidator } from '../types/validators/message-validators.js';
 
 type ComplexType = { +ids: { +[string]: $ReadOnlyArray<string> } };
 
@@ -84,3 +86,36 @@
     ).toStrictEqual(serverData);
   });
 });
+
+describe('extractUserIDsFromPayload', () => {
+  it('should extract all user ids from payload', () => {
+    const payload = {
+      rawMessageInfos: [
+        {
+          type: 0,
+          threadID: '1000',
+          creatorID: '0',
+          time: 0,
+          text: 'test',
+          id: '2000',
+        },
+        {
+          type: 0,
+          threadID: '1000',
+          creatorID: '1',
+          time: 0,
+          text: 'test',
+          id: '2001',
+        },
+      ],
+      truncationStatuses: {},
+      userInfos: {
+        ['100']: { id: '100', username: 'test1' },
+        ['200']: { id: '200', username: 'test2' },
+      },
+    };
+    expect(
+      extractUserIDsFromPayload(fetchMessageInfosResponseValidator, payload),
+    ).toEqual(['0', '1', '100', '200']);
+  });
+});