diff --git a/lib/shared/dm-ops/dm-op-specs.js b/lib/shared/dm-ops/dm-op-specs.js
index 1a5450270..75af1f0dc 100644
--- a/lib/shared/dm-ops/dm-op-specs.js
+++ b/lib/shared/dm-ops/dm-op-specs.js
@@ -1,17 +1,19 @@
 // @flow
 
 import { createSidebarSpec } from './create-sidebar-spec.js';
 import { createThreadSpec } from './create-thread-spec.js';
 import type { DMOperationSpec } from './dm-op-spec.js';
+import { sendEditMessageSpec } from './send-edit-message-spec.js';
 import { sendReactionMessageSpec } from './send-reaction-message-spec.js';
 import { sendTextMessageSpec } from './send-text-message-spec.js';
 import { type DMOperationType, dmOperationTypes } from '../../types/dm-ops.js';
 
 export const dmOpSpecs: {
   +[DMOperationType]: DMOperationSpec<any>,
 } = Object.freeze({
   [dmOperationTypes.CREATE_THREAD]: createThreadSpec,
   [dmOperationTypes.CREATE_SIDEBAR]: createSidebarSpec,
   [dmOperationTypes.SEND_TEXT_MESSAGE]: sendTextMessageSpec,
   [dmOperationTypes.SEND_REACTION_MESSAGE]: sendReactionMessageSpec,
+  [dmOperationTypes.SEND_EDIT_MESSAGE]: sendEditMessageSpec,
 });
diff --git a/lib/shared/dm-ops/send-edit-message-spec.js b/lib/shared/dm-ops/send-edit-message-spec.js
new file mode 100644
index 000000000..51a65d241
--- /dev/null
+++ b/lib/shared/dm-ops/send-edit-message-spec.js
@@ -0,0 +1,46 @@
+// @flow
+
+import uuid from 'uuid';
+
+import type { DMOperationSpec } from './dm-op-spec.js';
+import type { DMSendEditMessageOperation } from '../../types/dm-ops.js';
+import { messageTypes } from '../../types/message-types-enum.js';
+import { updateTypes } from '../../types/update-types-enum.js';
+import type { ClientUpdateInfo } from '../../types/update-types.js';
+
+const sendEditMessageSpec: DMOperationSpec<DMSendEditMessageOperation> =
+  Object.freeze({
+    processDMOperation: async (
+      dmOperation: DMSendEditMessageOperation,
+      viewerID: string,
+    ) => {
+      const { threadID, creatorID, time, messageID, targetMessageID, text } =
+        dmOperation;
+      const editMessage = {
+        type: messageTypes.EDIT_MESSAGE,
+        id: messageID,
+        threadID,
+        creatorID,
+        time,
+        targetMessageID,
+        text,
+      };
+
+      const updateInfos: Array<ClientUpdateInfo> = [];
+      if (creatorID !== viewerID) {
+        updateInfos.push({
+          type: updateTypes.UPDATE_THREAD_READ_STATUS,
+          id: uuid.v4(),
+          time,
+          threadID,
+          unread: true,
+        });
+      }
+      return {
+        rawMessageInfos: [editMessage],
+        updateInfos,
+      };
+    },
+  });
+
+export { sendEditMessageSpec };
diff --git a/lib/types/dm-ops.js b/lib/types/dm-ops.js
index f64e74d2e..97b7ef6f5 100644
--- a/lib/types/dm-ops.js
+++ b/lib/types/dm-ops.js
@@ -1,133 +1,156 @@
 // @flow
 
 import type { TInterface, TUnion } from 'tcomb';
 import t from 'tcomb';
 
 import type { RawMessageInfo } from './message-types.js';
 import {
   type NonSidebarThickThreadType,
   nonSidebarThickThreadTypes,
 } from './thread-types-enum.js';
 import type { ClientUpdateInfo } from './update-types.js';
 import { values } from '../utils/objects.js';
 import { tShape, tString, tUserID } from '../utils/validation-utils.js';
 
 export const dmOperationTypes = Object.freeze({
   CREATE_THREAD: 'create_thread',
   CREATE_SIDEBAR: 'create_sidebar',
   SEND_TEXT_MESSAGE: 'send_text_message',
   SEND_REACTION_MESSAGE: 'send_reaction_message',
+  SEND_EDIT_MESSAGE: 'send_edit_message',
 });
 export type DMOperationType = $Values<typeof dmOperationTypes>;
 
 export type DMCreateThreadOperation = {
   +type: 'create_thread',
   +threadID: string,
   +creatorID: string,
   +time: number,
   +threadType: NonSidebarThickThreadType,
   +memberIDs: $ReadOnlyArray<string>,
   +roleID: string,
   +newMessageID: string,
 };
 export const dmCreateThreadOperationValidator: TInterface<DMCreateThreadOperation> =
   tShape<DMCreateThreadOperation>({
     type: tString(dmOperationTypes.CREATE_THREAD),
     threadID: t.String,
     creatorID: tUserID,
     time: t.Number,
     threadType: t.enums.of(values(nonSidebarThickThreadTypes)),
     memberIDs: t.list(tUserID),
     roleID: t.String,
     newMessageID: t.String,
   });
 
 export type DMCreateSidebarOperation = {
   +type: 'create_sidebar',
   +threadID: string,
   +creatorID: string,
   +time: number,
   +parentThreadID: string,
   +memberIDs: $ReadOnlyArray<string>,
   +sourceMessageID: string,
   +roleID: string,
   +newSidebarSourceMessageID: string,
   +newCreateSidebarMessageID: string,
 };
 export const dmCreateSidebarOperationValidator: TInterface<DMCreateSidebarOperation> =
   tShape<DMCreateSidebarOperation>({
     type: tString(dmOperationTypes.CREATE_SIDEBAR),
     threadID: t.String,
     creatorID: tUserID,
     time: t.Number,
     parentThreadID: t.String,
     memberIDs: t.list(tUserID),
     sourceMessageID: t.String,
     roleID: t.String,
     newSidebarSourceMessageID: t.String,
     newCreateSidebarMessageID: t.String,
   });
 
 export type DMSendTextMessageOperation = {
   +type: 'send_text_message',
   +threadID: string,
   +creatorID: string,
   +time: number,
   +messageID: string,
   +text: string,
 };
 export const dmSendTextMessageOperationValidator: TInterface<DMSendTextMessageOperation> =
   tShape<DMSendTextMessageOperation>({
     type: tString(dmOperationTypes.SEND_TEXT_MESSAGE),
     threadID: t.String,
     creatorID: tUserID,
     time: t.Number,
     messageID: t.String,
     text: t.String,
   });
 
 export type DMSendReactionMessageOperation = {
   +type: 'send_reaction_message',
   +threadID: string,
   +creatorID: string,
   +time: number,
   +messageID: string,
   +targetMessageID: string,
   +reaction: string,
   +action: 'add_reaction' | 'remove_reaction',
 };
 export const dmSendReactionMessageOperationValidator: TInterface<DMSendReactionMessageOperation> =
   tShape<DMSendReactionMessageOperation>({
     type: tString(dmOperationTypes.SEND_REACTION_MESSAGE),
     threadID: t.String,
     creatorID: tUserID,
     time: t.Number,
     messageID: t.String,
     targetMessageID: t.String,
     reaction: t.String,
     action: t.enums.of(['add_reaction', 'remove_reaction']),
   });
 
+export type DMSendEditMessageOperation = {
+  +type: 'send_edit_message',
+  +threadID: string,
+  +creatorID: string,
+  +time: number,
+  +messageID: string,
+  +targetMessageID: string,
+  +text: string,
+};
+export const dmSendEditMessageOperationValidator: TInterface<DMSendEditMessageOperation> =
+  tShape<DMSendEditMessageOperation>({
+    type: tString(dmOperationTypes.SEND_EDIT_MESSAGE),
+    threadID: t.String,
+    creatorID: tUserID,
+    time: t.Number,
+    messageID: t.String,
+    targetMessageID: t.String,
+    text: t.String,
+  });
+
 export type DMOperation =
   | DMCreateThreadOperation
   | DMCreateSidebarOperation
   | DMSendTextMessageOperation
-  | DMSendReactionMessageOperation;
+  | DMSendReactionMessageOperation
+  | DMSendEditMessageOperation;
 export const dmOperationValidator: TUnion<DMOperation> = t.union([
   dmCreateThreadOperationValidator,
   dmCreateSidebarOperationValidator,
   dmSendTextMessageOperationValidator,
   dmSendReactionMessageOperationValidator,
+  dmSendEditMessageOperationValidator,
 ]);
 
 export type DMOperationResult = {
   rawMessageInfos: Array<RawMessageInfo>,
   updateInfos: Array<ClientUpdateInfo>,
 };
 
 export const processDMOpsActionType = 'PROCESS_DM_OPS';
 
 export type ProcessDMOpsPayload = {
   +rawMessageInfos: $ReadOnlyArray<RawMessageInfo>,
   +updateInfos: $ReadOnlyArray<ClientUpdateInfo>,
 };