diff --git a/keyserver/src/responders/redux-state-responders.js b/keyserver/src/responders/redux-state-responders.js
--- a/keyserver/src/responders/redux-state-responders.js
+++ b/keyserver/src/responders/redux-state-responders.js
@@ -1,27 +1,61 @@
 // @flow
 
-import t, { type TInterface } from 'tcomb';
+import _keyBy from 'lodash/fp/keyBy.js';
+import t from 'tcomb';
+import type { TInterface } from 'tcomb';
 
+import { baseLegalPolicies } from 'lib/facts/policies.js';
+import { daysToEntriesFromEntryInfos } from 'lib/reducers/entry-reducer.js';
+import { freshMessageStore } from 'lib/reducers/message-reducer.js';
+import { mostRecentlyReadThread } from 'lib/selectors/thread-selectors.js';
+import { mostRecentMessageTimestamp } from 'lib/shared/message-utils.js';
+import {
+  threadHasPermission,
+  threadIsPending,
+  parsePendingThreadID,
+  createPendingThread,
+} from 'lib/shared/thread-utils.js';
 import {
   entryStoreValidator,
   calendarQueryValidator,
 } from 'lib/types/entry-types.js';
+import { defaultCalendarFilters } from 'lib/types/filter-types.js';
 import { inviteLinksStoreValidator } from 'lib/types/link-types.js';
-import { messageStoreValidator } from 'lib/types/message-types.js';
+import {
+  defaultNumberPerThread,
+  messageStoreValidator,
+} from 'lib/types/message-types.js';
+import { threadPermissions } from 'lib/types/thread-permission-types.js';
+import { threadTypes } from 'lib/types/thread-types-enum.js';
 import { threadStoreValidator } from 'lib/types/thread-types.js';
 import {
   currentUserInfoValidator,
   userInfosValidator,
 } from 'lib/types/user-types.js';
+import { currentDateInTimeZone } from 'lib/utils/date-utils.js';
+import { promiseAll } from 'lib/utils/promises.js';
 import type { URLInfo } from 'lib/utils/url-utils.js';
-import { tShape } from 'lib/utils/validation-utils.js';
+import { tShape, ashoatKeyserverID } from 'lib/utils/validation-utils.js';
 import { navInfoValidator } from 'web/types/nav-types.js';
 import type {
   InitialReduxState,
   InitialKeyserverInfo,
 } from 'web/types/redux-types.js';
+import { navInfoFromURL } from 'web/url-utils.js';
 
-import type { Viewer } from '../session/viewer';
+import { fetchEntryInfos } from '../fetchers/entry-fetchers.js';
+import { fetchPrimaryInviteLinks } from '../fetchers/link-fetchers.js';
+import { fetchMessageInfos } from '../fetchers/message-fetchers.js';
+import { hasAnyNotAcknowledgedPolicies } from '../fetchers/policy-acknowledgment-fetchers.js';
+import { fetchThreadInfos } from '../fetchers/thread-fetchers.js';
+import {
+  fetchCurrentUserInfo,
+  fetchKnownUserInfos,
+  fetchUserInfos,
+} from '../fetchers/user-fetchers.js';
+import { getWebPushConfig } from '../push/providers.js';
+import { setNewSession } from '../session/cookies.js';
+import { Viewer } from '../session/viewer.js';
 
 const initialKeyserverInfoValidator = tShape<InitialKeyserverInfo>({
   sessionID: t.maybe(t.String),
@@ -44,12 +78,258 @@
     keyserverInfo: initialKeyserverInfoValidator,
   });
 
-/* eslint-disable no-unused-vars */
 async function getInitialReduxStateResponder(
   viewer: Viewer,
   urlInfo: URLInfo,
 ): Promise<InitialReduxState> {
-  return ({}: any);
+  const hasNotAcknowledgedPoliciesPromise = hasAnyNotAcknowledgedPolicies(
+    viewer.id,
+    baseLegalPolicies,
+  );
+
+  const initialNavInfoPromise = (async () => {
+    let backupInfo = {
+      now: currentDateInTimeZone(viewer.timeZone),
+    };
+    // Some user ids in selectedUserList might not exist in the userInfos
+    // (e.g. they were included in the results of the user search endpoint)
+    // Because of that we keep their userInfos inside the navInfo.
+    if (urlInfo.selectedUserList) {
+      const fetchedUserInfos = await fetchUserInfos(urlInfo.selectedUserList);
+      const userInfos = {};
+      for (const userID in fetchedUserInfos) {
+        const userInfo = fetchedUserInfos[userID];
+        if (userInfo.username) {
+          userInfos[userID] = userInfo;
+        }
+      }
+      backupInfo = { userInfos, ...backupInfo };
+    }
+    return navInfoFromURL(urlInfo, backupInfo);
+  })();
+
+  const calendarQueryPromise = (async () => {
+    const initialNavInfo = await initialNavInfoPromise;
+    return {
+      startDate: initialNavInfo.startDate,
+      endDate: initialNavInfo.endDate,
+      filters: defaultCalendarFilters,
+    };
+  })();
+  const messageSelectionCriteria = { joinedThreads: true };
+  const initialTime = Date.now();
+
+  const threadInfoPromise = fetchThreadInfos(viewer);
+  const messageInfoPromise = fetchMessageInfos(
+    viewer,
+    messageSelectionCriteria,
+    defaultNumberPerThread,
+  );
+  const entryInfoPromise = (async () => {
+    const calendarQuery = await calendarQueryPromise;
+    return await fetchEntryInfos(viewer, [calendarQuery]);
+  })();
+  const currentUserInfoPromise = fetchCurrentUserInfo(viewer);
+  const userInfoPromise = fetchKnownUserInfos(viewer);
+
+  const sessionIDPromise = (async () => {
+    const calendarQuery = await calendarQueryPromise;
+    if (viewer.loggedIn) {
+      await setNewSession(viewer, calendarQuery, initialTime);
+    }
+    return viewer.sessionID;
+  })();
+
+  const threadStorePromise = (async () => {
+    const [{ threadInfos }, hasNotAcknowledgedPolicies] = await Promise.all([
+      threadInfoPromise,
+      hasNotAcknowledgedPoliciesPromise,
+    ]);
+    return { threadInfos: hasNotAcknowledgedPolicies ? {} : threadInfos };
+  })();
+  const messageStorePromise = (async () => {
+    const [
+      { threadInfos },
+      { rawMessageInfos, truncationStatuses },
+      hasNotAcknowledgedPolicies,
+    ] = await Promise.all([
+      threadInfoPromise,
+      messageInfoPromise,
+      hasNotAcknowledgedPoliciesPromise,
+    ]);
+    if (hasNotAcknowledgedPolicies) {
+      return {
+        messages: {},
+        threads: {},
+        local: {},
+        currentAsOf: { [ashoatKeyserverID]: 0 },
+      };
+    }
+    const { messageStore: freshStore } = freshMessageStore(
+      rawMessageInfos,
+      truncationStatuses,
+      mostRecentMessageTimestamp(rawMessageInfos, initialTime),
+      threadInfos,
+    );
+    return freshStore;
+  })();
+  const entryStorePromise = (async () => {
+    const [{ rawEntryInfos }, hasNotAcknowledgedPolicies] = await Promise.all([
+      entryInfoPromise,
+      hasNotAcknowledgedPoliciesPromise,
+    ]);
+    if (hasNotAcknowledgedPolicies) {
+      return {
+        entryInfos: {},
+        daysToEntries: {},
+        lastUserInteractionCalendar: 0,
+      };
+    }
+    return {
+      entryInfos: _keyBy('id')(rawEntryInfos),
+      daysToEntries: daysToEntriesFromEntryInfos(rawEntryInfos),
+      lastUserInteractionCalendar: initialTime,
+    };
+  })();
+  const userInfosPromise = (async () => {
+    const [userInfos, hasNotAcknowledgedPolicies] = await Promise.all([
+      userInfoPromise,
+      hasNotAcknowledgedPoliciesPromise,
+    ]);
+    return hasNotAcknowledgedPolicies ? {} : userInfos;
+  })();
+
+  const navInfoPromise = (async () => {
+    const [
+      { threadInfos },
+      messageStore,
+      currentUserInfo,
+      userInfos,
+      finalNavInfo,
+    ] = await Promise.all([
+      threadInfoPromise,
+      messageStorePromise,
+      currentUserInfoPromise,
+      userInfosPromise,
+      initialNavInfoPromise,
+    ]);
+
+    const requestedActiveChatThreadID = finalNavInfo.activeChatThreadID;
+    if (
+      requestedActiveChatThreadID &&
+      !threadIsPending(requestedActiveChatThreadID) &&
+      !threadHasPermission(
+        threadInfos[requestedActiveChatThreadID],
+        threadPermissions.VISIBLE,
+      )
+    ) {
+      finalNavInfo.activeChatThreadID = null;
+    }
+
+    if (!finalNavInfo.activeChatThreadID) {
+      const mostRecentThread = mostRecentlyReadThread(
+        messageStore,
+        threadInfos,
+      );
+      if (mostRecentThread) {
+        finalNavInfo.activeChatThreadID = mostRecentThread;
+      }
+    }
+
+    if (
+      finalNavInfo.activeChatThreadID &&
+      threadIsPending(finalNavInfo.activeChatThreadID) &&
+      finalNavInfo.pendingThread?.id !== finalNavInfo.activeChatThreadID
+    ) {
+      const pendingThreadData = parsePendingThreadID(
+        finalNavInfo.activeChatThreadID,
+      );
+      if (
+        pendingThreadData &&
+        pendingThreadData.threadType !== threadTypes.SIDEBAR &&
+        currentUserInfo.id
+      ) {
+        const members = [...pendingThreadData.memberIDs, currentUserInfo.id]
+          .map(id => {
+            const userInfo = userInfos[id];
+            if (!userInfo || !userInfo.username) {
+              return undefined;
+            }
+            const { username } = userInfo;
+            return { id, username };
+          })
+          .filter(Boolean);
+        const newPendingThread = createPendingThread({
+          viewerID: currentUserInfo.id,
+          threadType: pendingThreadData.threadType,
+          members,
+        });
+        finalNavInfo.activeChatThreadID = newPendingThread.id;
+        finalNavInfo.pendingThread = newPendingThread;
+      }
+    }
+
+    return finalNavInfo;
+  })();
+  const currentAsOfPromise = (async () => {
+    const hasNotAcknowledgedPolicies = await hasNotAcknowledgedPoliciesPromise;
+    return hasNotAcknowledgedPolicies ? 0 : initialTime;
+  })();
+
+  const pushApiPublicKeyPromise = (async () => {
+    const pushConfig = await getWebPushConfig();
+    if (!pushConfig) {
+      if (process.env.NODE_ENV !== 'development') {
+        console.warn('keyserver/secrets/web_push_config.json should exist');
+      }
+      return null;
+    }
+    return pushConfig.publicKey;
+  })();
+
+  const inviteLinksStorePromise = (async () => {
+    const primaryInviteLinks = await fetchPrimaryInviteLinks(viewer);
+    const links = {};
+    for (const link of primaryInviteLinks) {
+      if (link.primary) {
+        links[link.communityID] = {
+          primaryLink: link,
+        };
+      }
+    }
+    return {
+      links,
+    };
+  })();
+
+  const keyserverInfoPromise = (async () => {
+    const { sessionID, updatesCurrentAsOf } = await promiseAll({
+      sessionID: sessionIDPromise,
+      updatesCurrentAsOf: currentAsOfPromise,
+    });
+
+    return {
+      sessionID,
+      updatesCurrentAsOf,
+    };
+  })();
+
+  const initialReduxState: InitialReduxState = await promiseAll({
+    navInfo: navInfoPromise,
+    currentUserInfo: currentUserInfoPromise,
+    entryStore: entryStorePromise,
+    threadStore: threadStorePromise,
+    userInfos: userInfosPromise,
+    actualizedCalendarQuery: calendarQueryPromise,
+    messageStore: messageStorePromise,
+    dataLoaded: viewer.loggedIn,
+    pushApiPublicKey: pushApiPublicKeyPromise,
+    commServicesAccessToken: null,
+    inviteLinksStore: inviteLinksStorePromise,
+    keyserverInfo: keyserverInfoPromise,
+  });
+
+  return initialReduxState;
 }
 
 export { getInitialReduxStateResponder };