Hosts - ExtensionPoint

<VersionOverrides> 
   <Hosts> 
      <Host xsi:type="Workbook"> 
         <DesktopFormFactor> 
            <ExtensionPoint xsi:type="PrimaryCommandSurface"> 

Hosts - ExtensionPoint - CommandSurface

Commands

PrimaryCommandSurface

The ribbon at the top.

<ExtensionPoint xsi:type="PrimaryCommandSurface"> 

MessageReadCommandSurface

The mail read view task pane window

<ExtensionPoint xsi:type="MessageReadCommandSurface"> 

MessageComposeCommandSurface

The mail compose form task pane window

<ExtensionPoint xsi:type="MessageComposeCommandSurface"> 

AppointmentOrganizerCommandSurface

<ExtensionPoint xsi:type="AppointmentOrganizerCommandSurface"> 

AppointmentAttendeeCommandSurface

<ExtensionPoint xsi:type="AppointmentAttendeeCommandSurface"> 

Module

Outlook only
Module extensibility lets you create new modules inside Outlook

<DesktopFormFactor> 
<ExtensionPoint xsi:type = "Module"> 
   <SourceLocation> 
   <Label> 
   <CommandSurface> 
      <Control xsi:type="Button" 
               id="custombutton"> 
      <Label> 
      <Action xsi:type="ExecuteFunction"> 
          <FunctionName> 
      </Action> 

Hosts - ExtensionPoint - CustomPane

<ExtensionPoint xsi:type="CustomPane"> 

SourceLocation - Required. The URL for the source code file of the add-in. This refers to a Url element in the Resources element.
Rule - Required. The rule or collection of rules that specify when the add-in activates. It is the same as defined in Outlook add-in manifests, except the ItemIs rule has the following changes: ItemType is either "Message" or "AppointmentAttendee", and there is no FormType attribute. For more information, see Custom pane Outlook add-ins and Activation rules for Outlook add-ins.
RequestedHeight - Optional. The requested height, in pixels, for the display pane when it is running on a desktop computer. This can be from 32 to 450 pixels. It is the same as in read add-ins (see RequestedHeight element (ItemReadTabletMailAppSettings complexType) (app manifest schema v1.1)
DisableEntityHighlighting - Optional. Specifies whether entity highlighting should be turned off for this mail add-in.

Hosts - ExtensionPoint - ContextMenu

<ExtensionPoint xsi:type="ContextMenu"> 
<OfficeMenu id="ContextMenuCell"> 
   <Control xsi:type="Menu"> 

The following two context menus are currently supported:
Excel - ContextMenuCell
Word - ContextMenuText

Hosts - ExtensionPoint - CustomFunctions

Custom Functions

<Hosts> 
<Host xsi:type="Workbook"> 
<AllFormFactors> 
<ExtensionPoint xsi:type="CustomFunctions">