diff --git a/lib/types/thread-types.js b/lib/types/thread-types.js
index ded07035d..9e197cc92 100644
--- a/lib/types/thread-types.js
+++ b/lib/types/thread-types.js
@@ -1,399 +1,399 @@
 // @flow
 
 import invariant from 'invariant';
 import PropTypes from 'prop-types';
 
 import type { Shape } from './core';
 import type {
   CalendarQuery,
   CalendarResult,
   RawEntryInfo,
 } from './entry-types';
 import type {
   RawMessageInfo,
   MessageTruncationStatuses,
 } from './message-types';
 import type { ClientThreadInconsistencyReportCreationRequest } from './report-types';
 import type { ThreadSubscription } from './subscription-types';
 import type { UpdateInfo } from './update-types';
 import type { UserInfo, AccountUserInfo } from './user-types';
 
 export const threadTypes = Object.freeze({
   //OPEN: 0,   (DEPRECATED)
   //CLOSED: 1, (DEPRECATED)
   //SECRET: 2, (DEPRECATED)
   CHAT_NESTED_OPEN: 3,
   CHAT_SECRET: 4,
   SIDEBAR: 5,
   PERSONAL: 6,
 });
 export type ThreadType = $Values<typeof threadTypes>;
 export function assertThreadType(threadType: number): ThreadType {
   invariant(
     threadType === 3 ||
       threadType === 4 ||
       threadType === 5 ||
       threadType === 6,
     'number is not ThreadType enum',
   );
   return threadType;
 }
 
 export const threadPermissions = Object.freeze({
   KNOW_OF: 'know_of',
   VISIBLE: 'visible',
   VOICED: 'voiced',
   EDIT_ENTRIES: 'edit_entries',
   EDIT_THREAD: 'edit_thread',
   DELETE_THREAD: 'delete_thread',
   CREATE_SUBTHREADS: 'create_subthreads',
   CREATE_SIDEBARS: 'create_sidebars',
   JOIN_THREAD: 'join_thread',
   EDIT_PERMISSIONS: 'edit_permissions',
   ADD_MEMBERS: 'add_members',
   REMOVE_MEMBERS: 'remove_members',
   CHANGE_ROLE: 'change_role',
   LEAVE_THREAD: 'leave_thread',
 });
 export type ThreadPermission = $Values<typeof threadPermissions>;
 export function assertThreadPermissions(
   ourThreadPermissions: string,
 ): ThreadPermission {
   invariant(
     ourThreadPermissions === 'know_of' ||
       ourThreadPermissions === 'visible' ||
       ourThreadPermissions === 'voiced' ||
       ourThreadPermissions === 'edit_entries' ||
       ourThreadPermissions === 'edit_thread' ||
       ourThreadPermissions === 'delete_thread' ||
       ourThreadPermissions === 'create_subthreads' ||
       ourThreadPermissions === 'create_sidebars' ||
       ourThreadPermissions === 'join_thread' ||
       ourThreadPermissions === 'edit_permissions' ||
       ourThreadPermissions === 'add_members' ||
       ourThreadPermissions === 'remove_members' ||
       ourThreadPermissions === 'change_role' ||
       ourThreadPermissions === 'leave_thread',
     'string is not threadPermissions enum',
   );
   return ourThreadPermissions;
 }
 
 export const threadPermissionPrefixes = Object.freeze({
   DESCENDANT: 'descendant_',
   CHILD: 'child_',
   OPEN: 'open_',
   OPEN_DESCENDANT: 'descendant_open_',
 });
 
 export type ThreadPermissionInfo =
   | {| value: true, source: string |}
   | {| value: false, source: null |};
 
 export type ThreadPermissionsBlob = {
   [permission: string]: ThreadPermissionInfo,
 };
 export type ThreadRolePermissionsBlob = { [permission: string]: boolean };
 
 export type ThreadPermissionsInfo = {
   [permission: ThreadPermission]: ThreadPermissionInfo,
 };
 export const threadPermissionsInfoPropType = PropTypes.objectOf(
   PropTypes.oneOfType([
     PropTypes.shape({
       value: PropTypes.oneOf([true]),
       source: PropTypes.string.isRequired,
     }),
     PropTypes.shape({
       value: PropTypes.oneOf([false]),
       source: PropTypes.oneOf([null]),
     }),
   ]),
 );
 
 export type MemberInfo = {|
   id: string,
   role: ?string,
   permissions: ThreadPermissionsInfo,
 |};
 export const memberInfoPropType = PropTypes.shape({
   id: PropTypes.string.isRequired,
   role: PropTypes.string,
   permissions: threadPermissionsInfoPropType.isRequired,
 });
 
 export type RelativeMemberInfo = {|
   ...MemberInfo,
   username: ?string,
   isViewer: boolean,
 |};
 export const relativeMemberInfoPropType = PropTypes.shape({
   id: PropTypes.string.isRequired,
   role: PropTypes.string,
   permissions: threadPermissionsInfoPropType.isRequired,
   username: PropTypes.string,
   isViewer: PropTypes.bool.isRequired,
 });
 
 export type RoleInfo = {|
   id: string,
   name: string,
   permissions: ThreadRolePermissionsBlob,
   isDefault: boolean,
 |};
 
 export type ThreadCurrentUserInfo = {|
   role: ?string,
   permissions: ThreadPermissionsInfo,
   subscription: ThreadSubscription,
   unread: ?boolean,
 |};
 
 export type RawThreadInfo = {|
   id: string,
   type: ThreadType,
   name: ?string,
   description: ?string,
   color: string, // hex, without "#" or "0x"
   creationTime: number, // millisecond timestamp
   parentThreadID: ?string,
   members: $ReadOnlyArray<MemberInfo>,
   roles: { [id: string]: RoleInfo },
   currentUser: ThreadCurrentUserInfo,
   sourceMessageID?: ?string,
 |};
 
 export type ThreadInfo = {|
   id: string,
   type: ThreadType,
   name: ?string,
   uiName: string,
   description: ?string,
   color: string, // hex, without "#" or "0x"
   creationTime: number, // millisecond timestamp
   parentThreadID: ?string,
   members: $ReadOnlyArray<MemberInfo>,
   roles: { [id: string]: RoleInfo },
   currentUser: ThreadCurrentUserInfo,
   sourceMessageID?: ?string,
 |};
 
 export const threadTypePropType = PropTypes.oneOf([
   threadTypes.CHAT_NESTED_OPEN,
   threadTypes.CHAT_SECRET,
   threadTypes.SIDEBAR,
   threadTypes.PERSONAL,
 ]);
 
 const rolePropType = PropTypes.shape({
   id: PropTypes.string.isRequired,
   name: PropTypes.string.isRequired,
   permissions: PropTypes.objectOf(PropTypes.bool).isRequired,
   isDefault: PropTypes.bool.isRequired,
 });
 
 const currentUserPropType = PropTypes.shape({
   role: PropTypes.string,
   permissions: threadPermissionsInfoPropType.isRequired,
   subscription: PropTypes.shape({
     pushNotifs: PropTypes.bool.isRequired,
     home: PropTypes.bool.isRequired,
   }).isRequired,
   unread: PropTypes.bool,
 });
 
 export const rawThreadInfoPropType = PropTypes.shape({
   id: PropTypes.string.isRequired,
   type: threadTypePropType.isRequired,
   name: PropTypes.string,
   description: PropTypes.string,
   color: PropTypes.string.isRequired,
   creationTime: PropTypes.number.isRequired,
   parentThreadID: PropTypes.string,
   members: PropTypes.arrayOf(memberInfoPropType).isRequired,
   roles: PropTypes.objectOf(rolePropType).isRequired,
   currentUser: currentUserPropType.isRequired,
   sourceMessageID: PropTypes.string,
 });
 
 export const threadInfoPropType = PropTypes.shape({
   id: PropTypes.string.isRequired,
   type: threadTypePropType.isRequired,
   name: PropTypes.string,
   uiName: PropTypes.string.isRequired,
   description: PropTypes.string,
   color: PropTypes.string.isRequired,
   creationTime: PropTypes.number.isRequired,
   parentThreadID: PropTypes.string,
   members: PropTypes.arrayOf(memberInfoPropType).isRequired,
   roles: PropTypes.objectOf(rolePropType).isRequired,
   currentUser: currentUserPropType.isRequired,
   sourceMessageID: PropTypes.string,
 });
 
 export type ServerMemberInfo = {|
   id: string,
   role: ?string,
   permissions: ThreadPermissionsInfo,
   subscription: ThreadSubscription,
   unread: ?boolean,
 |};
 
 export type ServerThreadInfo = {|
   id: string,
   type: ThreadType,
   name: ?string,
   description: ?string,
   color: string, // hex, without "#" or "0x"
   creationTime: number, // millisecond timestamp
   parentThreadID: ?string,
   members: $ReadOnlyArray<ServerMemberInfo>,
   roles: { [id: string]: RoleInfo },
   sourceMessageID?: ?string,
 |};
 
 export type ThreadStore = {|
   threadInfos: { [id: string]: RawThreadInfo },
   inconsistencyReports: $ReadOnlyArray<ClientThreadInconsistencyReportCreationRequest>,
 |};
 
 export type ThreadDeletionRequest = {|
   threadID: string,
   accountPassword: string,
 |};
 
 export type RemoveMembersRequest = {|
   threadID: string,
   memberIDs: $ReadOnlyArray<string>,
 |};
 
 export type RoleChangeRequest = {|
   threadID: string,
   memberIDs: $ReadOnlyArray<string>,
   role: string,
 |};
 
 export type ChangeThreadSettingsResult = {|
   threadInfo?: RawThreadInfo,
   threadInfos?: { [id: string]: RawThreadInfo },
   updatesResult: {
     newUpdates: $ReadOnlyArray<UpdateInfo>,
   },
   newMessageInfos: $ReadOnlyArray<RawMessageInfo>,
 |};
 
 export type ChangeThreadSettingsPayload = {|
   threadID: string,
   updatesResult: {
     newUpdates: $ReadOnlyArray<UpdateInfo>,
   },
   newMessageInfos: $ReadOnlyArray<RawMessageInfo>,
 |};
 
 export type LeaveThreadRequest = {|
   threadID: string,
 |};
 export type LeaveThreadResult = {|
   threadInfos?: { [id: string]: RawThreadInfo },
   updatesResult: {
     newUpdates: $ReadOnlyArray<UpdateInfo>,
   },
 |};
 
 export type LeaveThreadPayload = {|
   updatesResult: {
     newUpdates: $ReadOnlyArray<UpdateInfo>,
   },
 |};
 
 export type ThreadChanges = Shape<{|
   type: ThreadType,
   name: string,
   description: string,
   color: string,
   parentThreadID: string,
   newMemberIDs: $ReadOnlyArray<string>,
 |}>;
 
 export type UpdateThreadRequest = {|
   threadID: string,
   changes: ThreadChanges,
 |};
 
 export type BaseNewThreadRequest = {|
   +name?: ?string,
   +description?: ?string,
   +color?: ?string,
   +parentThreadID?: ?string,
   +initialMemberIDs?: ?$ReadOnlyArray<string>,
 |};
 export type NewThreadRequest =
   | {|
       +type: 3 | 4 | 6,
       ...BaseNewThreadRequest,
     |}
   | {|
       +type: 5,
-      +initialMessageID: string,
+      +sourceMessageID: string,
       ...BaseNewThreadRequest,
     |};
 
 export type NewThreadResponse = {|
   +updatesResult: {|
     +newUpdates: $ReadOnlyArray<UpdateInfo>,
   |},
   +newMessageInfos: $ReadOnlyArray<RawMessageInfo>,
   +newThreadInfo?: RawThreadInfo,
   +userInfos: { [string]: AccountUserInfo },
   +newThreadID?: string,
 |};
 export type NewThreadResult = {|
   +updatesResult: {|
     +newUpdates: $ReadOnlyArray<UpdateInfo>,
   |},
   +newMessageInfos: $ReadOnlyArray<RawMessageInfo>,
   +userInfos: { [string]: AccountUserInfo },
   +newThreadID: string,
 |};
 
 export type ServerThreadJoinRequest = {|
   threadID: string,
   calendarQuery?: ?CalendarQuery,
 |};
 export type ClientThreadJoinRequest = {|
   threadID: string,
   calendarQuery: CalendarQuery,
 |};
 export type ThreadJoinResult = {|
   threadInfos?: { [id: string]: RawThreadInfo },
   updatesResult: {
     newUpdates: $ReadOnlyArray<UpdateInfo>,
   },
   rawMessageInfos: $ReadOnlyArray<RawMessageInfo>,
   truncationStatuses: MessageTruncationStatuses,
   userInfos: { [string]: AccountUserInfo },
   rawEntryInfos?: ?$ReadOnlyArray<RawEntryInfo>,
 |};
 export type ThreadJoinPayload = {|
   updatesResult: {
     newUpdates: $ReadOnlyArray<UpdateInfo>,
   },
   rawMessageInfos: RawMessageInfo[],
   truncationStatuses: MessageTruncationStatuses,
   userInfos: $ReadOnlyArray<UserInfo>,
   calendarResult: CalendarResult,
 |};
 
 export type SidebarInfo = {|
   +threadInfo: ThreadInfo,
   +lastUpdatedTime: number,
   +mostRecentNonLocalMessage: ?string,
 |};
 
 // We can show a max of 3 sidebars inline underneath their parent in the chat
 // tab. If there are more, we show a button that opens a modal to see the rest
 export const maxReadSidebars = 3;
 
 // We can show a max of 5 sidebars inline underneath their parent
 // in the chat tab if every one of the displayed sidebars is unread
 export const maxUnreadSidebars = 5;
diff --git a/server/src/responders/thread-responders.js b/server/src/responders/thread-responders.js
index d785cad1d..318f8acdf 100644
--- a/server/src/responders/thread-responders.js
+++ b/server/src/responders/thread-responders.js
@@ -1,182 +1,182 @@
 // @flow
 
 import t from 'tcomb';
 
 import {
   type ThreadDeletionRequest,
   type RoleChangeRequest,
   type ChangeThreadSettingsResult,
   type RemoveMembersRequest,
   type LeaveThreadRequest,
   type LeaveThreadResult,
   type UpdateThreadRequest,
   type NewThreadRequest,
   type NewThreadResponse,
   type ServerThreadJoinRequest,
   type ThreadJoinResult,
   threadTypes,
 } from 'lib/types/thread-types';
 import { values } from 'lib/utils/objects';
 
 import createThread from '../creators/thread-creator';
 import { deleteThread } from '../deleters/thread-deleters';
 import type { Viewer } from '../session/viewer';
 import {
   updateRole,
   removeMembers,
   leaveThread,
   updateThread,
   joinThread,
 } from '../updaters/thread-updaters';
 import {
   validateInput,
   tShape,
   tNumEnum,
   tColor,
   tPassword,
 } from '../utils/validation-utils';
 import {
   entryQueryInputValidator,
   verifyCalendarQueryThreadIDs,
 } from './entry-responders';
 
 const threadDeletionRequestInputValidator = tShape({
   threadID: t.String,
   accountPassword: tPassword,
 });
 
 async function threadDeletionResponder(
   viewer: Viewer,
   input: any,
 ): Promise<LeaveThreadResult> {
   const request: ThreadDeletionRequest = input;
   await validateInput(viewer, threadDeletionRequestInputValidator, request);
   return await deleteThread(viewer, request);
 }
 
 const roleChangeRequestInputValidator = tShape({
   threadID: t.String,
   memberIDs: t.list(t.String),
   role: t.refinement(t.String, (str) => {
     const int = parseInt(str, 10);
     return int == str && int > 0;
   }),
 });
 
 async function roleUpdateResponder(
   viewer: Viewer,
   input: any,
 ): Promise<ChangeThreadSettingsResult> {
   const request: RoleChangeRequest = input;
   await validateInput(viewer, roleChangeRequestInputValidator, request);
   return await updateRole(viewer, request);
 }
 
 const removeMembersRequestInputValidator = tShape({
   threadID: t.String,
   memberIDs: t.list(t.String),
 });
 
 async function memberRemovalResponder(
   viewer: Viewer,
   input: any,
 ): Promise<ChangeThreadSettingsResult> {
   const request: RemoveMembersRequest = input;
   await validateInput(viewer, removeMembersRequestInputValidator, request);
   return await removeMembers(viewer, request);
 }
 
 const leaveThreadRequestInputValidator = tShape({
   threadID: t.String,
 });
 
 async function threadLeaveResponder(
   viewer: Viewer,
   input: any,
 ): Promise<LeaveThreadResult> {
   const request: LeaveThreadRequest = input;
   await validateInput(viewer, leaveThreadRequestInputValidator, request);
   return await leaveThread(viewer, request);
 }
 
 const updateThreadRequestInputValidator = tShape({
   threadID: t.String,
   changes: tShape({
     type: t.maybe(tNumEnum(values(threadTypes))),
     name: t.maybe(t.String),
     description: t.maybe(t.String),
     color: t.maybe(tColor),
     parentThreadID: t.maybe(t.String),
     newMemberIDs: t.maybe(t.list(t.String)),
   }),
   accountPassword: t.maybe(tPassword),
 });
 
 async function threadUpdateResponder(
   viewer: Viewer,
   input: any,
 ): Promise<ChangeThreadSettingsResult> {
   const request: UpdateThreadRequest = input;
   await validateInput(viewer, updateThreadRequestInputValidator, request);
   return await updateThread(viewer, request);
 }
 
 const threadRequestValidationShape = {
   name: t.maybe(t.String),
   description: t.maybe(t.String),
   color: t.maybe(tColor),
   parentThreadID: t.maybe(t.String),
   initialMemberIDs: t.maybe(t.list(t.String)),
 };
 const newThreadRequestInputValidator = t.union([
   tShape({
     type: tNumEnum([threadTypes.SIDEBAR]),
-    initialMessageID: t.String,
+    sourceMessageID: t.String,
     ...threadRequestValidationShape,
   }),
   tShape({
     type: tNumEnum([
       threadTypes.CHAT_NESTED_OPEN,
       threadTypes.CHAT_SECRET,
       threadTypes.PERSONAL,
     ]),
     ...threadRequestValidationShape,
   }),
 ]);
 async function threadCreationResponder(
   viewer: Viewer,
   input: any,
 ): Promise<NewThreadResponse> {
   const request: NewThreadRequest = input;
   await validateInput(viewer, newThreadRequestInputValidator, request);
   return await createThread(viewer, request);
 }
 
 const joinThreadRequestInputValidator = tShape({
   threadID: t.String,
   calendarQuery: t.maybe(entryQueryInputValidator),
 });
 async function threadJoinResponder(
   viewer: Viewer,
   input: any,
 ): Promise<ThreadJoinResult> {
   const request: ServerThreadJoinRequest = input;
   await validateInput(viewer, joinThreadRequestInputValidator, request);
 
   if (request.calendarQuery) {
     await verifyCalendarQueryThreadIDs(request.calendarQuery);
   }
 
   return await joinThread(viewer, request);
 }
 
 export {
   threadDeletionResponder,
   roleUpdateResponder,
   memberRemovalResponder,
   threadLeaveResponder,
   threadUpdateResponder,
   threadCreationResponder,
   threadJoinResponder,
   newThreadRequestInputValidator,
 };
diff --git a/server/src/responders/thread-responders.test.js b/server/src/responders/thread-responders.test.js
index 13ef336a9..ff9f226c3 100644
--- a/server/src/responders/thread-responders.test.js
+++ b/server/src/responders/thread-responders.test.js
@@ -1,53 +1,53 @@
 // @flow
 
 import { threadTypes } from 'lib/types/thread-types';
 
 import { newThreadRequestInputValidator } from './thread-responders';
 
 describe('Thread responders', () => {
   describe('New thread request validator', () => {
     const requestWithoutMessageID = {
       name: 'name',
       description: 'description',
       color: 'aaaaaa',
       parentThreadID: 'parentID',
       initialMemberIDs: [],
     };
     const requestWithMessageID = {
       ...requestWithoutMessageID,
-      initialMessageID: 'messageID',
+      sourceMessageID: 'messageID',
     };
 
-    it('Should require initialMessageID of a sidebar', () => {
+    it('Should require sourceMessageID of a sidebar', () => {
       expect(
         newThreadRequestInputValidator.is({
           type: threadTypes.SIDEBAR,
           ...requestWithoutMessageID,
         }),
       ).toBe(false);
 
       expect(
         newThreadRequestInputValidator.is({
           type: threadTypes.SIDEBAR,
           ...requestWithMessageID,
         }),
       ).toBe(true);
     });
 
-    it('Should not require initialMessageID of not a sidebar', () => {
+    it('Should not require sourceMessageID of not a sidebar', () => {
       expect(
         newThreadRequestInputValidator.is({
           type: threadTypes.CHAT_SECRET,
           ...requestWithoutMessageID,
         }),
       ).toBe(true);
 
       expect(
         newThreadRequestInputValidator.is({
           type: threadTypes.CHAT_SECRET,
           ...requestWithMessageID,
         }),
       ).toBe(false);
     });
   });
 });