What's the difference? Com/VSTO Add-in versus Office Add-in
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Microsoft Office 365 Integrations: The competitive difference between COM/VSTO Add-ins and Office Add-ins


How often do you think about how your email management system integrates with Outlook? Probably not very often, if ever. But you might want to think about it more if your current email management system is bogging down or crashing Outlook; isn’t available on Outlook web, Mac, or mobile; or requires a lot of IT help to set up and get running.

What does it mean to have a Microsoft Office 365 integration?

There are two ways to have a Microsoft Office 365 integration: through the COM/VSTO add-in or an Office Add-in.

The naming convention Microsoft has chosen can make it a little confusing to easily understand what kind of integration a vendor you’re evaluating offers because both add-in models can be called “Microsoft Office 365 integrations”. However, integrations done via COM/VSTO add-ins vs the Office Add-in platform are very different. Both have advantages, and it is important to understand them so you can pick the right solution for your organization’s email management needs.

What’s the difference between the COM/VSTO add-ins vs the Office Add-ins?

COM/VSTO add-ins

Historically, the primary method of integrating with Outlook has been via the COM or VSTO add-ins. This legacy model is very mature and has been around for a long time.

  • Requires local code running on each user’s device as well as a local install which is susceptible to environmental variables and potential conflicts with other add-ins.
  • Can be heavy and slow down Outlook because it relies on the same memory and CPU as Outlook.
  • Only available to Outlook desktop running on windows.
  • Can consume a lot of an organization’s internal IT resources to deploy, update, and maintain since there’s no centralized deployment or distribution.
  • Microsoft currently offers broader vendor customization for COM/VSTO add-ins, though this will change over time as Microsoft matures the Office Add-in platform.

Office Add-ins

The Office Add-in platform is Microsoft’s new approach to add-ins within MS Office applications. It solves many of the challenges with COM/VSTO add-ins and are essentially a web page that displays within the MS Office application, within Outlook in the case of ndMail.

  • True web- or cloud-based solution.
  • Brings flexibility and functionality to Outlook without bogging it down.
  • Can be deployed with just a few clicks to all your users.
  • Cross-platform for all devices that Microsoft Office 365 supports: web, Windows, Mac, iPad, and mobile (iOS and Android).
  • Doesn’t require a local install on any device.

What kind of Microsoft Office 365 integrations are available with ndMail?

ndMail has always been integrated with Microsoft Office 365 via the COM/VSTO add-in model. That integration allowed users of Outlook desktop for Windows to intelligently save, file, and manage email using artificial intelligence to generate cloud-based filing predictions and much more.

Now, NetDocuments is excited to announce that we’ve expanded our integrations with the release of ndMail for Office 365 which utilizes Office Add-ins and brings additional access and ease of use to more ndMail users.

Learn more about the benefits of ndMail for Office 365 Add-in here.

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