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Microsoft is Disabling Outlook COM and VSTO Add-Ins in 2024

Will the upcoming end of Outlook VSTO add-in and COM add-in Outlook extensions disrupt your organization? Don’t panic, you have options.
Written by: Penny Swift
outlook plugins
Published: February 13, 2024
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2024 heralds major changes for Microsoft users. Microsoft will be disabling its classic Outlook email client COM and VSTO add-ins, which will have major implications for many users. 

If you buy a Windows 11 device, it’ll be shipped with the new Outlook for Windows. If you have an older device, you can continue to download Mail, Calendar, and People applications until the end of the year. Then you’ll need to switch to the new Outlook, use classic Outlook without support, or opt for an alternative software app to access and manage your email messages.  

While the new Outlook will be a free-for-all-to-use default mailbox application, those who have been using the old Outlook VSTO add-in and COM add-in that used to come with Windows will have a problem. Because these add-ins won’t be supported anymore, they will soon be redundant. 

The obvious option is to transition to the new Outlook for Windows that Microsoft has introduced. But another option is to find an email solution that works equally well, if not better –  for example, a cloud-based email platform like Cerkl Broadcast. In any case, there is no doubt that cloud-based solutions offer all sorts of benefits including accessibility, data syncing, and collaboration features.

Email for Communications

We know that effective internal communication increases productivity. We also know that email remains the primary communication tool used by businesses globally. 

Grammarly’s The State of Business Communication in 2023 research conducted for the company by the Harris Poll on behalf of Grammarly shows that effective communication is the key to business performance. Nearly ¾ of the business leaders surveyed (72%) highlighted this factor, and 52% of knowledge workers agreed. 

The survey also shows that 72% of the workweek involves communicating with others. There has also been an increase in verbal communication: 15.95 hours vs 11.43 hours spent on verbal communication. But time spent on asynchronous communication platforms, including email, has also increased — by 21%. Furthermore, considerably more time is spent on email than any other form of communication, as the chart below (based on Grammarly figures) shows.

time spent on communication

According to Statista, by January 2022, 92% of the U.S. “digital population” was using emails as a form of communication. In comparison, 83% were using social media and 67% other online messaging apps. The number of email users worldwide was 4.26 billion, a figure they project will reach about 4.73 billion by 2026

Laura Ceci, a researcher at Statista highlights the fact that email has evolved from simply being a networking tool to “a valuable marketing strategy.” 

Nowadays, organizations have a huge choice when it comes to email services. According to Statista, in 2022, Apple’s devices using client Mail Privacy Protection (MPP), which hides iOS, iPadOS, and macOS devices for privacy purposes, were the most popular on the global market. They boasted 53.7% opens during the year. The Gmail client ranked second, with around 28% of email opens in 2022. Outlook ranked third with about 4.4% of the total global email opens. 

Microsoft Outlook vs Gmail

6sense compares Outlook and Gmail, which compete in current customers, market share, and category ranking. They found that Outlook has a 40.36% market share in the email management category – a little more than Gmail’s 36.05% market share. At the time, Outlook had 3,374,708 customers in 10 countries while Gmail had 3,015,012 customers in 10 countries. However, Gmail had more customers in the U.S., while Outlook had more customers in the U.S., UK, and Germany combined. 

After acquiring Hotmail in 1996, Microsoft replaced it in 2012. Within a year, Outlook.com had 400 million active users. The company moved the service to an Office 365-based infrastructure three years later, and two years after that launched a redesigned user interface. 

Gmail was launched as a service for its employees in 2004. By 2012, they already had 425  million active users.

It’ll be interesting to see the impact of the demise of Outlook VSTO add-in and COM add-in Outlook extensions on Outlook, Gmail, and other options.

Of course, the Outlook figures quoted here relate specifically to the old, classic Outlook. While some people will be happy to switch to the new Outlook email client, many aren’t. Even though the new Outlook supports web add-ins that Microsoft says have similar functionalities to COM and VSTO add-ins, it’s not the same. As a result, there is a trending term on social media, “the new Outlook sucks.” 

Why Do We Use Outlook Add-Ins?

There are various reasons for using Microsoft Outlook add-ins: 

  • Customization: Users can customize and extend the functionality of Microsoft Outlook based on their specific needs and workflow.
  • Automation: Add-ins allow for the automation of repetitive tasks, such as processing emails, updating calendar events, or interacting with external systems.
  • Integration: Add-ins facilitate integration with other applications and services, enhancing the overall productivity of users.
  • Business Logic: Developers can implement custom business logic within the add-ins to address specific requirements or industry workflows.
  • User Experience: Add-ins can improve the user experience by providing additional features, insights, or tools directly within the Outlook interface.

Many major internal communications platforms base their email offering on Outlook, allowing clients to use the add-ins. However, they do vary. For example, PoliteMail allows the new Outlook add-ins and the COM add-ins but they don’t use any VSTO add-ins. 

Staffbase has instructions for those using the classic Outlook as well as Outlook 365 and Outlook for Mac. Contact Monkey has instructions on how to link to Outlook without obvious details on which version you will be linking to. 

However, it’s doubtful that this approach will be tenable in the medium term. Indications are that with the changes Microsoft has introduced, the entire industry is poised to migrate to cloud platforms. 

What are Outlook COM Add-Ins?

Outlook COM add-ins are based on the component object model (COM), a Microsoft technology for building binary software components. These add-ins are usually developed using languages like C++ or C# with COM interop. 

The COM add-in Outlook extension interacts directly with the Outlook application through the COM interface. This allows developers to extend and customize Outlook’s functionality.

COM add-ins are suitable for scenarios that need deep integration with Outlook. They can access the Outlook object model to manipulate items, folders, and other aspects of the application.

What are Outlook VSTO Add-Ins?

An Outlook VSTO add-in extension is built using Visual Studio Tools for Office, which is an extension of the .NET framework. These add-ins are typically developed using C# or VB.NET.

VSTO add-ins provide a higher-level, managed code approach to building Outlook extensions. They provide a more developer-friendly environment compared to COM add-ins.

Additionally, VSTO Add-ins are suitable for developers who prefer working with managed code and want to leverage the .NET framework. They provide a more streamlined development experience and are often chosen for business productivity solutions.

outlook com vs outlook vsto

Difference between COM and VSTO Add-ins

While both COM and Outlook VSTO add-ins extend the functionality of Outlook, VSTO offers a more modern and developer-friendly approach with managed code, seamless integration with the .NET Framework, and simplified deployment. The choice between the two depends on factors such as the developer’s preference, the complexity of the project, and the desired level of integration with Outlook.

Here are some key differences between the two.

Approach to Technology and Development

COM add-ins are developed using languages like C++ or C# with COM interop. They are based on the component object model (COM), a Microsoft technology for building binary software components. And they require a more low-level approach to interacting with Outlook’s object model.

VSTO add-ins are developed using C# or VB.NET within the Visual Studio environment. They utilize Visual Studio Tools for Office (VSTO), which is an extension of the .NET Framework. They also provide a higher-level, managed code approach to building Outlook extensions.

Ease of Development

Outlook COM add-ins generally involve more complex and lower-level coding compared to VSTO. Developers need to manage COM interop and handle memory management more explicitly.

Outlook VSTO add-ins offer a more developer-friendly environment. They simplify development with managed code, automatic garbage collection, and a more modern programming model.

Integration and Interoperability

COM add-ins interact directly with Outlook through the COM interface. They can also have deeper integration with Outlook’s object model.

VSTO add-ins leverage the .NET Framework and provide seamless integration with other .NET technologies. They offer a higher-level abstraction, making it easier to work with Outlook features.


Deployment of a COM add-in Outlook may involve registering DLLs and dealing with registry entries. They can be more complex and manual compared to VSTO deployment.

Deployment of a VSTO add-in is typically more straightforward using ClickOnce technology. Generally, it offers a more streamlined deployment process with automatic updates.

Platform Support

Historically, COM is a Windows-specific technology, and COM add-ins may have limited cross-platform compatibility.

VSTO add-ins, on the other hand, can provide better support for cross-platform development, especially if targeting the .NET Core or .NET 5+ frameworks.

Development Environment

COM add-ins can be developed in various IDEs, including Visual Studio, but may require additional setup for COM interop.

VSTO add-ins are developed within Visual Studio using the VSTO tools, providing an integrated and streamlined development experience.

When choosing between a COM add-in Outlook works with and VSTO add-ins, developers consider certain relevant factors. These include their preferred programming language, development environment, and the level of integration required with Outlook’s object model. Additionally, the choice may be influenced by the complexity of the required functionality and the specific needs of the project.

outlook vsto addin vs com addin

Why Is Microsoft Disabling Them?

Microsoft says it’s improving the Outlook experience across platforms by unifying it into a single web codebase. They haven’t said much more about the decision to do this, though they do say they are providing “a more reliable and stable add-in experience.” This, they say, is why they aren’t continuing to support VSTO and COM add-ins. 

Most of the communication they have posted simply promotes the new Outlook for Windows, which they say has “a modern and simplified design.”

“You can tailor it to your style and do more with the new Outlook for Windows! Learn more about the new Outlook for Windows here.”


Without saying they are disabling (killing) the old classic Outlook COM and VSTO add-ins, Microsoft lists the benefits of the new Outlook. They state that the new Outlook for Windows is for everyone and you can get it free (with Windows). You can:

  • Streamline accounts
  • Stay on top of things
  • Feel secure
  • Accomplish more 
  • Stay organized
  • Unify your accounts

But what about all those users who don’t use Windows or Microsoft 365/Office 365? These include macOS users and other Android platforms.

“To ensure your add-in continues to work in the new Outlook on Windows, you must migrate your VSTO or COM add-in to an Outlook web add-in. Migrating to an Outlook web add-in not only enables compatibility with the new Outlook on Windows, it also makes your solution available to users on other platforms, such as Outlook on Mac, on mobile, or on the web.”


In other words, if you are using Outlook add-ins, you need to migrate to the new Outlook. End of story, it seems.   

How Will it Affect Your Outlook Plugin Email?

If you have an Outlook plugin email or Outlook add-ins users you are going to lose access to the additional features and functionalities provided by those add-ins. 

As we have said, Outlook add-ins enhance the email client by offering tools for automation, integration with third-party services, and customization. Users who rely on specific add-ins for tasks such as analytics, productivity, or collaboration would experience a reduction in functionality. Business workflows that depend on these add-ins for efficiency and productivity might be disrupted, requiring users to find alternative solutions or adapt to the native capabilities of Outlook. 

Ultimately, the impact will vary based on your reliance on the soon-to-be disabled add-ins.

Transition to the New Outlook or Not?

This is an open-ended question and the answers are varied. 

Microsoft has been encouraging users of the classic Outlook to switch to the new Outlook. It takes just one click and, at the moment (February 2024), you can switch between the two. But, Cornell University says it’s not a good idea — though only IT professionals can access the full story. 

“We do not recommend manually switching to the New Outlook. The New Outlook view is a test environment which lacks significant functionality.”

Cornell University

Writing in azcentral., which is part of the USA TODAY Network, Ken Colburn points out that the “new Outlook for Windows is an app, not a website that is free and has the basic look and feel of the paid versions of Outlook that have a lot more features.” As of July 31, when the article was published, he says that if you like the interface of the email app, you can continue to use it for at least the next year. He confirms that the indication is that it will be shelved towards the end of 2024. But …

“It’s obvious that they’re trying to create a pathway to convince users that are using their free tools to upgrade to their premium versions to generate revenue.”

Ken Colburn

Since you’re basically being forced to use the new Outlook for Windows, you might as well take the time to get used to it now, he says. But, “If you work at a company that uses Microsoft’s various platforms, the when and how to switch guidance should come from your IT department.”

Another option is to stay on the classic Outlook, but then you’ll have to come to terms with the fact that there will be no future updates and you may face compatibility issues.

Disadvantages of the new Outlook 

There are several obvious disadvantages of switching to the new Outlook. That’s why people are saying that “the new Outlook sucks.” They are simply disenchanted. 

  • You’ll be faced with a complete change in user interface and experience. Those accustomed to the classic Outlook may need time to adapt to the new interface and workflows, which can impact productivity.
  • The new web add-ins may not fully replicate functionality as Microsoft implies they will. The fact is that existing COM and VSTO add-ins — (Outlook VSTO add-in and COM add-in Outlook) — might not have direct web add-in equivalents. This will require alternative solutions or migration efforts.
  • There are potential compatibility issues. For example, some third-party tools or legacy workflows might not be fully compatible with the new Outlook software. 

Ultimately, the reality is that the use of Outlook for internal comms is now history. The obvious option is an intuitive, flexible cloud-based solution like Cerkl Broadcast. 

Cloud-Based & Web-Based Email Client Options

Web-based email options are a subset of cloud-based email services. Both provide advantages such as accessibility, convenience, and cross-platform compatibility. However, when people refer to “cloud-based email,” they often emphasize the broader cloud infrastructure, including features like scalability, reliability, and collaboration tools that go beyond the basic web-based email functionality.

More specifically, web-based email client options available allow users to access their emails through a web browser. These services are hosted on the Internet, providing convenience and accessibility from any device with an Internet connection. 

Other options include Yahoo, Zoho, ProtonMai, FastMail, Mail.com, and AOL mail. 

While the exact offerings of web-based email client options vary, they all have similar benefits. These include:

  • Accessibility: Users can access their emails from any device with a web browser and an internet connection.
  • Convenience: There is no need to install software. Users can log into their accounts from any location.
  • Cross-platform compatibility: They work on various operating systems without the need for specific software.

Cloud-based email services are hosted on cloud infrastructure, allowing for scalability, reliability, and accessibility from multiple devices. Primary benefits include:

  • Scalability: Cloud-based email services can scale resources based on demand, accommodating growing storage and user needs.
  • Reliability: Data is stored on redundant servers, reducing the risk of data loss due to hardware failures.
  • Collaboration: Many cloud-based email services offer integrated collaboration tools. These include shared calendars and document storage.
cloud based vs web based outlook

Outlook and Gmail — the biggest in the market — are both web-based and cloud-based. 

Users commonly choose their email services based on factors like user interface preferences, collaboration features, and integration with other tools and services.

What’s Next?

Cerkl Broadcast is a cloud-based email option rather than a client-based one. Our platform is hosted on remote servers but accessed through the internet – via a browser. And our Eblasts enable you to create high-impact email communications. 

You avoid the cost of a local server as well as other regular costs including staff, and other elements needed to support web-based platforms. Maintenance is a non-issue. Because it isn’t dependent on hardware, you have considerably more capacity and space for growth. 

Security is an obvious issue, but we work through Google Cloud, Microsoft Azure, and Amazon AWS, which give us the ability to protect your data. And, of course, we offer many other advantages. 

Hear more about your options and schedule a chat. 

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