Please follow the steps below to integrate. You've to integrate Microsoft Graph API to get IMAP service. 

• 2. Click on Manage > App registrations from left menu then click New registration.

• 3. After that, you'll get a form like this. Fill up as below. In Redirect URI, you should add this url https://yourdomain.com/index.php/microsoft_api/save_outlook_imap_access_token. You'll find this in your integration setting. Finally click on Register button.

• 4. Now, you'll get the Overview page. Copy Client ID from there and add to integration settings.

• 5. Click on API permissions from left menu. Then click on Add a permission.

• 6. Click on Microsoft Graph.

• 7. Click on Application permissions.

• 8. Search Mail.ReadWrite, OnPremisesPublishingProfiles, User.Read.All and enable the permissions.

• 9. Click on Certificates & secrets from left menu. Then click on New client secret.

• 10. Fill up the form like below and click on Add button.

• 11. After that, you'll get the Client secret.

• 12. Add this Client secret also to the integration settings and click on Save & authorize. The page will be redirected to Microsoft account. Click on the Accept button. 

• After redirect, please check the IMAP setting is Authorized.