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3 min readAug 14, 2024

Creating an Outlook Add-in to Invoke Backend APIs

Developing an Outlook add-in can greatly enhance productivity by integrating custom functionalities directly within the email client. This blog post will guide you through the process of creating an Outlook add-in that can invoke backend APIs, and we’ll discuss whether it can be installed on Office 365 Outlook.

What is an Outlook Add-in?

An Outlook add-in is a small web application that can be embedded within Outlook to extend its capabilities. These add-ins can interact with emails, calendar events, and other Outlook features to provide additional functionality, such as sending data to a backend API or displaying external data within Outlook.

Prerequisites

Node.js: Install the latest LTS version of Node.js from the official site.
Yeoman and the Office Add-in Generator: These tools help scaffold your add-in project.

npm install -g yo generator-office

Microsoft 365 Subscription: Ensure you have access to Outlook through a Microsoft 365 subscription.
Code Editor: Use Visual Studio Code or your preferred code editor.

Step-by-Step Guide

1. Create an Outlook Add-in Project

Use Yeoman Generator: Run the following command to scaffold a new Outlook add-in project.

yo office

Choose Project Type: Select “Office Add-in Task Pane project” when prompted.
Select Script Type: Choose “JavaScript” or “TypeScript” based on your preference.
Name Your Add-in: Provide a name for your add-in.
Select Office Client: Choose “Outlook” as the Office client application.

This will create a project structure with all the necessary files to start developing your add-in.

2. Develop the Add-in

Modify the Manifest: The manifest file (manifest.xml) defines how your add-in interacts with Outlook. You can specify the add-in's appearance, permissions, and the URLs it will use.
Implement Backend API Calls: In your add-in’s JavaScript or TypeScript files, implement the logic to call your backend APIs. You can use fetch or axios to make HTTP requests.

async function fetchData() {
    try {
        const response = await fetch('https://api.example.com/data');
        const data = await response.json();
        console.log(data);
    } catch (error) {
        console.error('Error fetching data:', error);
    }
}

UI Customization: Customize the task pane UI using HTML, CSS, and JavaScript to display data fetched from the backend.

3. Test the Add-in

Run the Add-in Locally: Use the following command to start a local server and sideload the add-in into Outlook.

npm start

Sideload the Add-in: Follow the instructions provided by the generator to sideload your add-in into Outlook for testing.

4. Deploy the Add-in

Host the Add-in: Once development is complete, host the add-in’s web application on a server that supports HTTPS.
Update the Manifest: Ensure the manifest file points to the correct URLs for your hosted add-in.
Distribute the Add-in: You can distribute your add-in through the Microsoft AppSource or by providing the manifest file to users for sideloading.

Can It Be Installed on Office 365 Outlook?

Yes, the add-in can be installed on Office 365 Outlook. Outlook add-ins are designed to work across various platforms, including Outlook on the web, Outlook for Windows, and Outlook for Mac, as long as they are connected to a Microsoft 365 account. This ensures that your add-in is accessible to users regardless of the platform they use.

Conclusion

Creating an Outlook add-in that interacts with backend APIs can significantly enhance the functionality of your email client. By following these steps, you can develop a custom add-in that integrates seamlessly with Outlook, providing users with powerful new capabilities. Whether you’re automating tasks or integrating external data, Outlook add-ins offer a flexible and robust solution for extending Outlook’s functionality.

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