diff --git a/lib/keyserver-conn/call-single-keyserver-endpoint.js b/lib/keyserver-conn/call-single-keyserver-endpoint.js
--- a/lib/keyserver-conn/call-single-keyserver-endpoint.js
+++ b/lib/keyserver-conn/call-single-keyserver-endpoint.js
@@ -202,7 +202,7 @@
       json = await Promise.race([callEndpointPromise, rejectPromise]);
     }
   }
-  extractAndPersistUserInfosFromEndpointResponse(json, endpoint);
+  extractAndPersistUserInfosFromEndpointResponse(json, endpoint, dispatch);
 
   const { cookieChange, error, payload, currentUserInfo } = json;
   const sessionChange: ?ServerSessionChange = cookieChange;
diff --git a/lib/socket/socket.react.js b/lib/socket/socket.react.js
--- a/lib/socket/socket.react.js
+++ b/lib/socket/socket.react.js
@@ -370,6 +370,7 @@
         <SocketMessageUserInfosHandler
           addListener={this.addListener}
           removeListener={this.removeListener}
+          dispatch={this.props.dispatch}
         />
       </React.Fragment>
     );
diff --git a/lib/socket/user-infos-handler.react.js b/lib/socket/user-infos-handler.react.js
--- a/lib/socket/user-infos-handler.react.js
+++ b/lib/socket/user-infos-handler.react.js
@@ -2,6 +2,8 @@
 
 import * as React from 'react';
 
+import { processNewUserIDsActionType } from '../actions/user-actions.js';
+import type { Dispatch } from '../types/redux-types.js';
 import {
   serverServerSocketMessageValidator,
   type SocketListener,
@@ -12,19 +14,27 @@
 type Props = {
   +addListener: (listener: SocketListener) => mixed,
   +removeListener: (listener: SocketListener) => mixed,
+  +dispatch: Dispatch,
 };
 
 export default function SocketMessageUserInfosHandler(
   props: Props,
 ): React.Node {
-  const onMessage = React.useCallback((message: ClientServerSocketMessage) => {
-    // eslint-disable-next-line no-unused-vars
-    const newUserIDs = extractUserIDsFromPayload(
-      serverServerSocketMessageValidator,
-      message,
-    );
-    // TODO: dispatch an action adding the new user ids to the UserStore
-  }, []);
+  const onMessage = React.useCallback(
+    (message: ClientServerSocketMessage) => {
+      const newUserIDs = extractUserIDsFromPayload(
+        serverServerSocketMessageValidator,
+        message,
+      );
+      if (newUserIDs.length > 0) {
+        props.dispatch({
+          type: processNewUserIDsActionType,
+          payload: { userIDs: newUserIDs },
+        });
+      }
+    },
+    [props],
+  );
 
   const { addListener, removeListener } = props;
 
diff --git a/lib/utils/user-info-extraction-utils.js b/lib/utils/user-info-extraction-utils.js
--- a/lib/utils/user-info-extraction-utils.js
+++ b/lib/utils/user-info-extraction-utils.js
@@ -3,9 +3,11 @@
 import _memoize from 'lodash/memoize.js';
 import t, { type TType, type TInterface } from 'tcomb';
 
+import { processNewUserIDsActionType } from '../actions/user-actions.js';
 import type { CallSingleKeyserverEndpointResponse } from '../keyserver-conn/call-single-keyserver-endpoint.js';
 import { mixedRawThreadInfoValidator } from '../permissions/minimally-encoded-raw-thread-info-validators.js';
 import type { Endpoint } from '../types/endpoints.js';
+import type { Dispatch } from '../types/redux-types.js';
 import type { MixedRawThreadInfos } from '../types/thread-types.js';
 import { userInfoValidator } from '../types/user-types.js';
 import type { UserInfo } from '../types/user-types.js';
@@ -73,13 +75,18 @@
 function extractAndPersistUserInfosFromEndpointResponse(
   message: CallSingleKeyserverEndpointResponse,
   endpoint: Endpoint,
+  dispatch: Dispatch,
 ): void {
   const extendedValidator = extendResponderValidator(
     endpointValidators[endpoint].validator,
   );
-  // eslint-disable-next-line no-unused-vars
   const newUserIDs = extractUserIDsFromPayload(extendedValidator, message);
-  // TODO: dispatch an action adding the new user ids to the UserStore
+  if (newUserIDs.length > 0) {
+    dispatch({
+      type: processNewUserIDsActionType,
+      payload: { userIDs: newUserIDs },
+    });
+  }
 }
 
 export { extractAndPersistUserInfosFromEndpointResponse };