Assistance Needed with Outlook Add-In installing Manifest for older version of Outlook

[docupile]

I'm currently working on developing an Outlook add-in for my organization. This add-in is designed to help users upload Outlook email attachments directly to our cloud server. However, I'm facing an issue while I am installing the Add-In then it successfully installed in Outlook new version, for Outlook older version with the same add-in manifest file, which is not displaying of the add-in in Microsoft® Outlook® for Microsoft 365 MSO (Version 2405 Build 16.0.17628.20006) 64-bit.

Steps Taken:

1. I have validated the XML structure using various XML validators.
2. I used the Office Add-in Validator, but it didn't highlight any issues.
3. I ensured that all URLs used in the manifest are accessible.
4. I simplified the manifest file to its basic elements, yet the issue persists.

Manifest File: Here is the actual manifest file with important URLs and IDs replaced with placeholders:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<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/1.0"
           xsi:type="MailApp">
  <Id>XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX</Id>
  <Version>1.0.0.1</Version>
  <ProviderName>Product Name Addin</ProviderName>
  <DefaultLocale>en-US</DefaultLocale>
  <DisplayName DefaultValue="Product Name Addin"/>
  <Description DefaultValue="This Addin helps to upload attachments to the server."/>
  <IconUrl DefaultValue="Icon-64x64.png"/>
  <HighResolutionIconUrl DefaultValue="Icon.png"/>
  <SupportUrl DefaultValue="https://learn.microsoft.com/office/dev/add-ins/overview/office-add-in-code-samples"/>
  <AppDomains>
    <AppDomain>https://www.domain.com</AppDomain>
  </AppDomains>
  <Hosts>
    <Host Name="Mailbox"/>
  </Hosts>
  <Requirements>
    <Sets>
      <Set Name="Mailbox" MinVersion="1.1"/>
    </Sets>
  </Requirements>
  <FormSettings>
    <Form xsi:type="ItemRead">
      <DesktopSettings>
        <SourceLocation DefaultValue="https://www.domain.com/login.html"/>
        <RequestedHeight>250</RequestedHeight>
      </DesktopSettings>
    </Form>
  </FormSettings>
  <Permissions>ReadWriteItem</Permissions>
  <Rule xsi:type="RuleCollection" Mode="Or">
    <Rule xsi:type="ItemIs" ItemType="Appointment" FormType="Edit"/>
    <Rule xsi:type="ItemIs" ItemType="Message" FormType="Edit"/>
  </Rule>
  <DisableEntityHighlighting>false</DisableEntityHighlighting>
  <VersionOverrides xmlns="http://schemas.microsoft.com/office/mailappversionoverrides" xsi:type="VersionOverridesV1_0">
    <Requirements>
      <bt:Sets DefaultMinVersion="1.1">
        <bt:Set Name="Mailbox"/>
      </bt:Sets>
    </Requirements>
    <Hosts>
      <Host xsi:type="MailHost">
        <DesktopFormFactor>
          <ExtensionPoint xsi:type="MessageReadCommandSurface">
            <OfficeTab id="TabDefault">
              <Group id="msgComposeCmdGroup">
                <Label resid="CommandsGroup.Label"/>
                <Control xsi:type="Button" id="msgComposeInsertGist">
                  <Label resid="TaskpaneButton.Label"/>
                  <Supertip>
                    <Title resid="TaskpaneButton.SupertipTitle"/>
                    <Description resid="TaskpaneButton.SupertipText"/>
                  </Supertip>
                  <Icon>
                    <bt:Image size="16" resid="Icon.16x16"/>
                    <bt:Image size="32" resid="Icon.32x32"/>
                    <bt:Image size="80" resid="Icon.80x80"/>
                  </Icon>
                  <Action xsi:type="ShowTaskpane">
                    <SourceLocation resid="Taskpane.Url"/>
                  </Action>
                </Control>
              </Group>
            </OfficeTab>
          </ExtensionPoint>
        </DesktopFormFactor>
      </Host>
    </Hosts>
    <Resources>
      <bt:Images>
        <bt:Image id="Icon.16x16" DefaultValue="icon16.ico"/>
        <bt:Image id="Icon.32x32" DefaultValue="icon32.ico"/>
        <bt:Image id="Icon.80x80" DefaultValue="icon80.ico"/>
      </bt:Images>
      <bt:Urls>
        <bt:Url id="Taskpane.Url" DefaultValue="https://www.domain.com/login.html"/>
      </bt:Urls>
      <bt:ShortStrings>
        <bt:String id="CommandsGroup.Label" DefaultValue="Attachment Add-in"/>
        <bt:String id="TaskpaneButton.Label" DefaultValue="Product Name"/>
        <bt:String id="TaskpaneButton.SupertipTitle" DefaultValue="Product Name Addin"/>
      </bt:ShortStrings>
      <bt:LongStrings>
        <bt:String id="TaskpaneButton.SupertipText" DefaultValue="Upload the attachments directly to the cloud."/>
      </bt:LongStrings>
    </Resources>
  </VersionOverrides>
</OfficeApp>

Request:

I would greatly appreciate any insights or suggestions to resolve this issue. Specifically, I'm looking for help to:

1. Identify any potential issues in the manifest file that might be causing the installation to fail.
2. Suggestions on additional debugging steps to capture more detailed error information from Outlook.
3. Any known compatibility issues with the Outlook version I'm using.

Thank you in advance for your help!

[normanzhao]

I am having the same issue and am wondering if it's because the certification team has to sideload the add-in in order to test it. As per the manual sideload instructions, it may take up to 24 hours to show because of caching issues

[Swathy-Mothilal]

@docupile Can you please confirm if you are still facing this issue? And from the description, are you facing this issue only in Outlook classic?

[docupile]

@Swathy-Mothilal Yes we are still facing the same issue with Outlook Classic. [Microsoft® Outlook® for Microsoft 365 MSO (Version 2405 Build 16.0.17628.20006) 64-bit]