diff --git a/lib/utils/action-utils.js b/lib/utils/action-utils.js
--- a/lib/utils/action-utils.js
+++ b/lib/utils/action-utils.js
@@ -22,6 +22,7 @@
 } from '../types/account-types.js';
 import type { PlatformDetails } from '../types/device-types.js';
 import type { Endpoint, SocketAPIHandler } from '../types/endpoints.js';
+import type { CalendarQuery } from '../types/entry-types.js';
 import type { LoadingOptions, LoadingInfo } from '../types/loading-types.js';
 import type {
   ActionPayload,
@@ -476,6 +477,52 @@
   return results;
 }
 
+function sortCalendarQueryPerKeyserver(
+  calendarQuery: CalendarQuery,
+  keyserverIDs: $ReadOnlyArray<string>,
+): {
+  +[keyserverID: string]: CalendarQuery,
+} {
+  const { startDate, endDate, filters } = calendarQuery;
+  const results = {};
+
+  for (const keyserverID of keyserverIDs) {
+    results[keyserverID] = {
+      startDate,
+      endDate,
+      filters: [],
+    };
+  }
+
+  for (const filter of filters) {
+    if (filter.type === 'not_deleted') {
+      for (const keyserverID in results) {
+        results[keyserverID].filters.push({ type: 'not_deleted' });
+      }
+    } else if (filter.type === 'threads') {
+      for (const threadID of filter.threadIDs) {
+        const keyserverID = extractKeyserverIDFromID(threadID);
+        if (results[keyserverID] === undefined) {
+          continue;
+        }
+        let threadFilter = results[keyserverID].filters.find(
+          flt => flt.type === 'threads',
+        );
+        if (!threadFilter) {
+          threadFilter = { type: 'threads', threadIDs: [] };
+          results[keyserverID].filters.push(threadFilter);
+        }
+
+        threadFilter.threadIDs.push(threadID);
+      }
+    } else {
+      console.warn('unhandled filter in sortCalendarQueryPerKeyserver');
+    }
+  }
+
+  return results;
+}
+
 export {
   useDispatchActionPromise,
   setNewSessionActionType,
@@ -486,4 +533,5 @@
   bindCookieAndUtilsIntoCallServerEndpoint,
   extractKeyserverIDFromID,
   sortThreadIDsPerKeyserver,
+  sortCalendarQueryPerKeyserver,
 };
diff --git a/lib/utils/action-utils.test.js b/lib/utils/action-utils.test.js
--- a/lib/utils/action-utils.test.js
+++ b/lib/utils/action-utils.test.js
@@ -1,6 +1,10 @@
 // @flow
 
-import { extractKeyserverIDFromID } from './action-utils.js';
+import {
+  extractKeyserverIDFromID,
+  sortCalendarQueryPerKeyserver,
+} from './action-utils.js';
+import type { CalendarQuery } from '../types/entry-types';
 
 describe('extractKeyserverIDFromID', () => {
   it('should return <keyserverID> for <keyserverID>|<number>', () => {
@@ -9,3 +13,71 @@
     expect(extractKeyserverIDFromID(id)).toBe(keyserverID);
   });
 });
+
+describe('sortCalendarQueryPerKeyserver', () => {
+  it('should split the calendar query into multiple queries, one for every \
+  keyserver, that have all the properties of the original one, \
+  but only the thread ids that the keyserver should get', () => {
+    const query: CalendarQuery = {
+      startDate: '1463588881886',
+      endDate: '1463588889886',
+      filters: [
+        { type: 'not_deleted' },
+        {
+          type: 'threads',
+          threadIDs: ['256|1', '256|2', '100|100', '100|101'],
+        },
+      ],
+    };
+    const queriesPerKeyserver = {
+      ['256']: {
+        startDate: '1463588881886',
+        endDate: '1463588889886',
+        filters: [
+          { type: 'not_deleted' },
+          {
+            type: 'threads',
+            threadIDs: ['256|1', '256|2'],
+          },
+        ],
+      },
+      ['100']: {
+        startDate: '1463588881886',
+        endDate: '1463588889886',
+        filters: [
+          { type: 'not_deleted' },
+          {
+            type: 'threads',
+            threadIDs: ['100|100', '100|101'],
+          },
+        ],
+      },
+    };
+    expect(sortCalendarQueryPerKeyserver(query, ['100', '256'])).toEqual(
+      queriesPerKeyserver,
+    );
+  });
+
+  it('should create calendar query for every keyserver in the second argument', () => {
+    const query: CalendarQuery = {
+      startDate: '1463588881886',
+      endDate: '1463588889886',
+      filters: [{ type: 'not_deleted' }],
+    };
+    const queriesPerKeyserver = {
+      ['256']: {
+        startDate: '1463588881886',
+        endDate: '1463588889886',
+        filters: [{ type: 'not_deleted' }],
+      },
+      ['100']: {
+        startDate: '1463588881886',
+        endDate: '1463588889886',
+        filters: [{ type: 'not_deleted' }],
+      },
+    };
+    expect(sortCalendarQueryPerKeyserver(query, ['100', '256'])).toEqual(
+      queriesPerKeyserver,
+    );
+  });
+});