Sending Emails using MS-Graph with list-unsubscribe headers

Question

Hi Team,

I am facing some issue where i am not able to add list unsubscribe headers without X- prefix using Microsoft graph API.
I have a use case where i want to add List-Unsubscribe and List-Unsubscribe-Post headers but when i try to add it to internetMessageHeaders it only allows headers with X- prefixes.
But for providers to automatically gets the List-Unsubscribe headers to show the Unsusbcribe button the key needs to be exact.

Do we have a way to add these headers to emails sent through Microsoft graph api?

Answer 1

To include List-Unsubscribe mail header, you need to add it via SingleValueExtendedProperties

using Microsoft.Graph.Me.SendMail;
using Microsoft.Graph.Models;

var requestBody = new SendMailPostRequestBody
{
	Message = new Message
	{
		Subject = "Meet for lunch?",
		Body = new ItemBody
		{
			ContentType = BodyType.Text,
			Content = "The new cafeteria is open.",
		},
		ToRecipients = new List<Recipient>
		{
			new Recipient
			{
				EmailAddress = new EmailAddress
				{
					Address = "johndoe@contoso.com",
				},
			},
		},
		SingleValueExtendedProperties = new List<SingleValueLegacyExtendedProperty>
		{
			new SingleValueLegacyExtendedProperty
			{
				Id = "String 0x1045",
				Value = "<mailto:unsubscribe@reply.contoso.com>, <https://contoso.com/notifications/unsubscribe/123>",
			},
		},
	},
};

If you need to include also List-Unsubscribe-Post, the solution is more complicated, because there is no way to add List-Unsubscribe-Post via SingleValueExtendedProperties. You need to send message in MIME format.

Great blog post how to create a MIME message for Graph API is here