Outlook Addin not appearing in Windows Outlook 365

Question

My addin is working in outlook web client as expected but not showing in Outlook 365 Windows client (Ribbon Buttons not appearing).

I double checked the manifest, it is working as expected on another tenant in Outlook Client (only different urls, Outlook Version 2009 - newer because in preview channel) but not in another (Outlook Version 1908 semi annual channel). Addin is activated and loading in the web client but not in Windows Client.

Manifest (changed names, urls and guid)

<?xml version="1.0" encoding="UTF-8"?>
<!-- Example + Schema: https://learn.microsoft.com/en-us/office/dev/add-ins/develop/add-in-manifests?tabs=tabid-3#manifest-v11-xml-file-examples-and-schemas -->

<OfficeApp
          xmlns="http://schemas.microsoft.com/office/appforoffice/1.1"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xmlns:bt="http://schemas.microsoft.com/office/officeappbasictypes/1.0"
          xmlns:mailappor="http://schemas.microsoft.com/office/mailappversionoverrides/1.1"
          xsi:type="MailApp">

  <Id>BDE022E4-6241-433F-2222-1BC250CE1E27</Id>
  <Version>3.3.0.0</Version>
  <ProviderName>Name</ProviderName>
  <DefaultLocale>de-DE</DefaultLocale>
  <!-- The display name of your add-in. Used on the store and various places of the Office UI such as the add-ins dialog. -->
  <DisplayName DefaultValue="AddinName" />
  <Description DefaultValue="Name AddinName Add-in"/>
    <IconUrl DefaultValue="https://url/OutlookAddin/assets/HT_Icons_DMS.png" />
  <HighResolutionIconUrl DefaultValue="https://url/OutlookAddin/assets/HT_Icons_DMS.png" />
  <SupportUrl DefaultValue="https://name.de/support" />

  <!-- Domains that will be allowed when navigating. For example, if you use ShowTaskpane and then have an href link, navigation will only be allowed if the domain is on this list. -->
  <AppDomains>
    <AppDomain>https://url</AppDomain>
  </AppDomains>
  <!--End Basic Settings. -->
  <Hosts>
    <Host Name="Mailbox" />
  </Hosts>
  <Requirements>
    <Sets>
      <Set Name="Mailbox" MinVersion="1.1" />
    </Sets>
  </Requirements>
  <FormSettings>
    <Form xsi:type="ItemRead">
      <DesktopSettings>
        <SourceLocation DefaultValue="https://url/OutlookAddin/index.html"/>
        <RequestedHeight>250</RequestedHeight>
      </DesktopSettings>
    </Form>
  </FormSettings>

  <Permissions>ReadWriteItem</Permissions>
  <Rule xsi:type="RuleCollection" Mode="Or">
    <Rule xsi:type="ItemIs" ItemType="Message" FormType="Read" />
    <Rule xsi:type="ItemIs" ItemType="Message" FormType="Edit" />
  </Rule>

  <VersionOverrides xmlns="http://schemas.microsoft.com/office/mailappversionoverrides" xsi:type="VersionOverridesV1_0">
    <Requirements>
      <bt:Sets DefaultMinVersion="1.3">
        <bt:Set Name="Mailbox" />
      </bt:Sets>
    </Requirements>
    <Hosts>
      <Host xsi:type="MailHost">
        <DesktopFormFactor>
          <!-- Location of the Functions that UI-less buttons can trigger (ExecuteFunction Actions). -->
          <FunctionFile resid="functionFile" />

          <!-- Message Read -->
          <ExtensionPoint xsi:type="MessageReadCommandSurface">
            <!-- Use the default tab of the ExtensionPoint or create your own with <CustomTab id="myTab"> -->
            <OfficeTab id="TabDefault">
              <!-- Up to 6 Groups added per Tab -->
              <Group id="msgReadGroup">
                <Label resid="readGroupLabel" />
                <!-- Launch the add-in : task pane button -->
                <Control xsi:type="Button" id="msgReadOpenPaneButton">
                  <Label resid="paneReadButtonLabel" />
                  <Supertip>
                    <Title resid="paneReadSuperTipTitle" />
                    <Description resid="paneReadSuperTipDescription" />
                  </Supertip>
                  <Icon>
                    <bt:Image size="16" resid="readicon16" />
                    <bt:Image size="32" resid="readicon32" />
                    <bt:Image size="80" resid="readicon80" />
                    <bt:Image size="96" resid="readicon96" />
                  </Icon>
                  <Action xsi:type="ShowTaskpane">
                    <SourceLocation resid="messageReadTaskPaneUrl" />
                  </Action>
                </Control>
                <!-- Go to http://aka.ms/ButtonCommands to learn how to add more Controls: ExecuteFunction and Menu -->
              </Group>
            </OfficeTab>
          </ExtensionPoint>
          <!-- Message compose form -->
          <ExtensionPoint xsi:type="MessageComposeCommandSurface">
            <OfficeTab id="TabDefault">
              <Group id="msgComposeGroup">
                <Label resid="composeGroupLabel" />
                <!-- Task pane button -->
                <Control xsi:type="Button" id="msgComposeOpenPaneButton">
                  <Label resid="paneComposeButtonLabel" />
                  <Supertip>
                    <Title resid="paneComposeSuperTipTitle" />
                    <Description resid="paneComposeSuperTipDescription" />
                  </Supertip>
                  <Icon>
                    <bt:Image size="16" resid="composeicon16" />
                    <bt:Image size="32" resid="composeicon32" />
                    <bt:Image size="80" resid="composeicon80" />
                    <bt:Image size="96" resid="composeicon96" />
                  </Icon>
                  <Action xsi:type="ShowTaskpane">
                    <SourceLocation resid="composeTaskPaneUrl" />
                  </Action>
                </Control>
              </Group>
            </OfficeTab>
          </ExtensionPoint>          
          <!-- Go to http://aka.ms/ExtensionPointsCommands to learn how to add more Extension Points: MessageRead, AppointmentOrganizer, AppointmentAttendee -->
        </DesktopFormFactor>
      </Host>
    </Hosts>
    <Resources>
      <bt:Images>
        <bt:Image id="readicon16" DefaultValue="https://url/OutlookAddin/assets/readicon-16.png"/>
        <bt:Image id="readicon32" DefaultValue="https://url/OutlookAddin/assets/readicon-32.png"/>
        <bt:Image id="readicon80" DefaultValue="https://url/OutlookAddin/assets/readicon-80.png"/>
        <bt:Image id="readicon96" DefaultValue="https://url/OutlookAddin/assets/readicon-96.png"/>
        <bt:Image id="composeicon16" DefaultValue="https://url/OutlookAddin/assets/composeicon-16.png"/>
        <bt:Image id="composeicon32" DefaultValue="https://url/OutlookAddin/assets/composeicon-32.png"/>
        <bt:Image id="composeicon80" DefaultValue="https://url/OutlookAddin/assets/composeicon-80.png"/>
        <bt:Image id="composeicon96" DefaultValue="https://url/OutlookAddin/assets/composeicon-96.png"/>
      </bt:Images>
      <bt:Urls>
        <bt:Url id="functionFile" DefaultValue="https://url/OutlookAddin/function-file/function-file.html"/>
        <bt:Url id="messageReadTaskPaneUrl" DefaultValue="https://url/OutlookAddin/index.html?mode=read"/>
        <bt:Url id="composeTaskPaneUrl" DefaultValue="https://url/OutlookAddin/index.html?mode=compose"/>
      </bt:Urls>
      <bt:ShortStrings>
        <bt:String id="readGroupLabel" DefaultValue="AddinName"/>
        <bt:String id="paneReadButtonLabel" DefaultValue="Hochladen"/>
        <bt:String id="paneReadSuperTipTitle" DefaultValue="AddinName"/>
        <bt:String id="composeGroupLabel" DefaultValue="AddinName"/>
        <bt:String id="paneComposeButtonLabel" DefaultValue="Attachment anfügen"/>
        <bt:String id="paneComposeSuperTipTitle" DefaultValue="AddinName"/>
      </bt:ShortStrings>
      <bt:LongStrings>
        <bt:String id="paneReadSuperTipDescription" DefaultValue="Name AddinName Add-in"/>
        <bt:String id="paneComposeSuperTipDescription" DefaultValue="Name AddinName Add-in"/>
      </bt:LongStrings>
    </Resources>
     <VersionOverrides xmlns="http://schemas.microsoft.com/office/mailappversionoverrides/1.1" xsi:type="VersionOverridesV1_1">
        <Requirements>
      <bt:Sets DefaultMinVersion="1.3">
        <bt:Set Name="Mailbox" />
      </bt:Sets>
    </Requirements>
    <Hosts>
      <Host xsi:type="MailHost">
        <DesktopFormFactor>
          <!-- Location of the Functions that UI-less buttons can trigger (ExecuteFunction Actions). -->
          <FunctionFile resid="functionFile" />

          <!-- Message Read -->
          <ExtensionPoint xsi:type="MessageReadCommandSurface">
            <!-- Use the default tab of the ExtensionPoint or create your own with <CustomTab id="myTab"> -->
            <OfficeTab id="TabDefault">
              <!-- Up to 6 Groups added per Tab -->
              <Group id="msgReadGroup">
                <Label resid="readGroupLabel" />
                <!-- Launch the add-in : task pane button -->
                <Control xsi:type="Button" id="msgReadOpenPaneButton">
                  <Label resid="paneReadButtonLabel" />
                  <Supertip>
                    <Title resid="paneReadSuperTipTitle" />
                    <Description resid="paneReadSuperTipDescription" />
                  </Supertip>
                  <Icon>
                    <bt:Image size="16" resid="readicon16" />
                    <bt:Image size="32" resid="readicon32" />
                    <bt:Image size="80" resid="readicon80" />
                    <bt:Image size="96" resid="readicon96" />
                  </Icon>
                  <Action xsi:type="ShowTaskpane">
                    <SourceLocation resid="messageReadTaskPaneUrl" />
                    <SupportsPinning>true</SupportsPinning>
                  </Action>
                </Control>
                <!-- Go to http://aka.ms/ButtonCommands to learn how to add more Controls: ExecuteFunction and Menu -->
              </Group>
            </OfficeTab>
          </ExtensionPoint>
           <!-- Message compose form -->
          <ExtensionPoint xsi:type="MessageComposeCommandSurface">
            <OfficeTab id="TabDefault">
              <Group id="msgComposeGroup">
                <Label resid="composeGroupLabel" />
                <!-- Task pane button -->
                <Control xsi:type="Button" id="msgComposeOpenPaneButton">
                  <Label resid="paneComposeButtonLabel" />
                  <Supertip>
                    <Title resid="paneComposeSuperTipTitle" />
                    <Description resid="paneComposeSuperTipDescription" />
                  </Supertip>
                  <Icon>
                    <bt:Image size="16" resid="composeicon16" />
                    <bt:Image size="32" resid="composeicon32" />
                    <bt:Image size="80" resid="composeicon80" />
                    <bt:Image size="96" resid="composeicon96" />
                  </Icon>
                  <Action xsi:type="ShowTaskpane">
                    <SourceLocation resid="composeTaskPaneUrl" />
                    <SupportsPinning>true</SupportsPinning>
                  </Action>
                </Control>
              </Group>
            </OfficeTab>
          </ExtensionPoint>
          <!-- Go to http://aka.ms/ExtensionPointsCommands to learn how to add more Extension Points: MessageRead, AppointmentOrganizer, AppointmentAttendee -->
        </DesktopFormFactor>
      </Host>
    </Hosts>

    <Resources>
      <bt:Images>
        <bt:Image id="readicon16" DefaultValue="https://url/OutlookAddin/assets/readicon-16.png"/>
        <bt:Image id="readicon32" DefaultValue="https://url/OutlookAddin/assets/readicon-32.png"/>
        <bt:Image id="readicon80" DefaultValue="https://url/OutlookAddin/assets/readicon-80.png"/>
        <bt:Image id="readicon96" DefaultValue="https://url/OutlookAddin/assets/readicon-96.png"/>
        <bt:Image id="composeicon16" DefaultValue="https://url/OutlookAddin/assets/composeicon-16.png"/>
        <bt:Image id="composeicon32" DefaultValue="https://url/OutlookAddin/assets/composeicon-32.png"/>
        <bt:Image id="composeicon80" DefaultValue="https://url/OutlookAddin/assets/composeicon-80.png"/>
        <bt:Image id="composeicon96" DefaultValue="https://url/OutlookAddin/assets/composeicon-96.png"/>
      </bt:Images>
      <bt:Urls>
        <bt:Url id="functionFile" DefaultValue="https://url/OutlookAddin/function-file/function-file.html"/>
        <bt:Url id="messageReadTaskPaneUrl" DefaultValue="https://url/OutlookAddin/index.html?mode=read"/>
        <bt:Url id="composeTaskPaneUrl" DefaultValue="https://url/OutlookAddin/index.html?mode=compose"/>
      </bt:Urls>
      <bt:ShortStrings>
        <bt:String id="readGroupLabel" DefaultValue="AddinName"/>
        <bt:String id="paneReadButtonLabel" DefaultValue="Hochladen"/>
        <bt:String id="paneReadSuperTipTitle" DefaultValue="AddinName"/>
        <bt:String id="composeGroupLabel" DefaultValue="AddinName"/>
        <bt:String id="paneComposeButtonLabel" DefaultValue="Attachment anfügen"/>
        <bt:String id="paneComposeSuperTipTitle" DefaultValue="AddinName"/>
      </bt:ShortStrings>
      <bt:LongStrings>
        <bt:String id="paneReadSuperTipDescription" DefaultValue="Name AddinName Add-in"/>
        <bt:String id="paneComposeSuperTipDescription" DefaultValue="Name AddinName Add-in"/>
      </bt:LongStrings>
    </Resources>
    </VersionOverrides>
  </VersionOverrides>
</OfficeApp>

What could be the problem? How can I troubleshoot what is happening? The obvious troubleshooting articles from microsoft did not help.

Edit: OnPremise Exchange 2016, Addin worked with other versions of outlook on windows (non 365 Versions)

Answer 1

Thanks to the hints that Outlook Add-ins Team - MSFT gave I found the solution to my problem:

It was indeed the privacy control setting in the registry that has been distributed by group policies. In our case especially the key

HKEY_CURRENT_USER\Software\Policies\Microsoft\office\16.0\common\privacy -> controllerconnectedservicesenabled

was set to dword:00000002 (which is disabled).

After I changed it to dword:00000001 (enabled) the Add-in immediately appeared!

The relevant information can be found at the bottom of this microsoft article https://learn.microsoft.com/en-us/deployoffice/privacy/manage-privacy-controls