Interacting with Outlook from an ASP.Net Core Blazor Web-site

Question

I am converting an old Silverlight application into Asp.Net Core, using Blazor and Razor Pages.

The old application is opening Outlook, and creating an email ready to send with a Subject, From etc, plus a series of attachments. It is creating an object to do this using the following code:

Dynamic outlook = AutomationFactory.GetObject(“Outlook.Application”).

In my web-site, I do something similar:

Use a COM reference to the Microsoft Outlook 16.0 object library.
If Outlook is already running, then get a reference to its associated “Outlook.Application” COM object as per https://renenyffenegger.ch/notes/Microsoft/dot-net/namespaces-classes/System/Runtime/InteropServices/Marshal/GetActiveObject.
Otherwise, create an object using Microsoft.Office.Interop.Outlook.Application appOutlook = new Microsoft.Office.Interop.Outlook.Application();

This works when running my web-site locally in Visual Studio, however I cannot deploy it to Azure:

C:\Program Files\dotnet\sdk\6.0.201\Microsoft.Common.CurrentVersion.targets(2926,5): Error : MSB4803: The task "ResolveComReference" is not supported on the .NET Core version of MSBuild. Please use the .NET Framework version of MSBuild. See https://aka.ms/msbuild/MSB4803 for further details.

I’m assuming that I won’t be able to use this approach, however I can’t see any alternative. Any suggestions as to how I can do this in an ASP.Net Core Blazor web-site would be greatly appreciated.

Dmitry Streblechenko · Accepted Answer · 2022-03-28 18:10:28Z

0

You cannot use Outlook, or any other Office app, in a service (such as IIS). Even if you do manage to make it run, it won't help you - your code is running on the server, and the message you populate and display will be on the server, where nobody would ever see it.

You can either use a mailto: link (it supports address, subject, and body) or (if you need HTML and/or attachments), dynamically create an EML (MIME) file - Outlook on the client side will be happy to open it. To make sure the message is editable, add X-Unsent: 1 MIME header.

answered Mar 28, 2022 at 18:10

Dmitry Streblechenko

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2 Comments

Geoff Olding Over a year ago

Many thanks for your replies. I won't be able to use "MailTo:", as I need to add attachments, and I need it to run on modern browsers. I don't need to send the email. We am not using JavaScript (it is a Blazor web-site). I guess I'll need to have a look at the "EML (MIME) file" approach, which is not something I've not used before. As I say, I need some way of making the process seamless - I need to be able to open Outlook and have it open up with the email that I have created, ready for the user to manually review\edit and send.

Dmitry Streblechenko Over a year ago

At the very least , the browser will prompt the user to open the file.

Eugene Astafiev · Accepted Answer · 2022-03-28 20:35:39Z

In my web-site, I do something similar: Use a COM reference to the Microsoft Outlook 16.0 object library.

The Considerations for server-side Automation of Office states the following:

Microsoft does not currently recommend, and does not support, Automation of Microsoft Office applications from any unattended, non-interactive client application or component (including ASP, ASP.NET, DCOM, and NT Services), because Office may exhibit unstable behavior and/or deadlock when Office is run in this environment.

If you are building a solution that runs in a server-side context, you should try to use components that have been made safe for unattended execution. Or, you should try to find alternatives that allow at least part of the code to run client-side. If you use an Office application from a server-side solution, the application will lack many of the necessary capabilities to run successfully. Additionally, you will be taking risks with the stability of your overall solution.

From a JS code you can automate Outlook from Internet Explorer (only on Windows). Other browsers don't know anything about the COM technology. So, I'd suggest considering other approaches for getting the work done. The easiest way, like Dmitry suggested, is to use the mailto protocol. It opens a client's e-mail system and begins a new email message. The following example shows a link that will prepare an e-mail message:

<a href="mailto:[email protected]?
    subject=MessageTitle&amp;
    body=Message Content">
    Contact Us</a>

You may consider using EWS or Graph API if you need to send email silently.

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