Outlook add-in doesn't open in shared mailboxes despite SupportsSharedFolders set to true

Question

Here's what we do:

• We create an add-in with the Yeoman generator as described here.
• We modify the manifest.xml to support shared folders:

...
<VersionOverrides xmlns="http://schemas.microsoft.com/office/mailappversionoverrides" xsi:type="VersionOverridesV1_0">
    <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>
            <SupportsSharedFolders>true</SupportsSharedFolders>
            <FunctionFile resid="Commands.Url"/>
            ...
  </VersionOverrides>
</VersionOverrides>

• We sideload the add-in in OWA for one user via manifest-file.
• We start a local development server with npm run dev-server.

The Add-in works perfectly in the user's own mailbox. But when we try to activate the add-in for a mail in a shared mailbox we get this pop-up-message:

"You cannot peform this action. This add-in scenario is not supported in this folder."

What do we have to do to get the add-in running in shared folders/mailboxes?

We're using Outlook-Client Version 2002 and Exchange 2016 15.01.1913.005. A call to Office.context.requirements.isSetSupported('Mailbox', '1.8') returns true.

Answer 1

add-in for shared folders/mailboxes requires Exchange support that is only enabled in Exchange online. Without Exchange support, such as the case with Exchange 2016, the behavior for the addin is the same as if the SupportsSharedFolders is not there. We will make sure this is clearly documented.