TL;DR

Add WelcomeEmailDisabled to resourceBehaviorOptions via AdditionalData when creating the group. It can only be set at creation time — not patched afterward.

AdditionalData = new Dictionary<string, object>
{
    { "resourceBehaviorOptions", new List<string> { "WelcomeEmailDisabled" } }
}

Want the full example with owners and members included? Read on. 👇

The Problem

When building automated site provisioning, every Microsoft 365 group creation triggers a welcome email to each member by default. In an automated scenario where multiple groups are created at once, that quickly turns into a flood of emails your users didn’t ask for — and they’re going to call it spam.

Microsoft documents WelcomeEmailDisabled as a supported option, but doesn’t show you how to actually set it from the Graph SDK in C#. That’s what this post is about.

The Weird Part: AdditionalData

If you look at the typed Group object in the SDK, you won’t find a ResourceBehaviorOptions property anywhere. It has to be set through AdditionalData — a catch-all dictionary for properties that exist in the Graph API but aren’t modeled as first-class typed properties in the SDK.

It works fine, but it does mean you lose IntelliSense and compile-time safety. The same pattern applies to owners@odata.bind and members@odata.bind, which let you assign owners and members at creation time without separate follow-up calls.

The Solution

Here’s the complete group creation request with welcome emails disabled, owners set, and members added — all in a single API call:

var ownerId = $"https://graph.microsoft.com/v1.0/users/{ownerObjectId}";
var groupMembers = new List<string>
{
    $"https://graph.microsoft.com/v1.0/users/{memberObjectId1}",
    $"https://graph.microsoft.com/v1.0/users/{memberObjectId2}"
};

Group requestBody = new()
{
    Description = description,
    DisplayName = displayName,
    GroupTypes = ["Unified"],
    MailEnabled = false,
    MailNickname = siteName,
    SecurityEnabled = true,
    AdditionalData = new Dictionary<string, object>
    {
        { "resourceBehaviorOptions", new List<string> { "WelcomeEmailDisabled" } },
        { "owners@odata.bind", new List<string> { ownerId } },
        { "members@odata.bind", groupMembers }
    }
};

Group? group = await _graphClient.Groups.PostAsync(requestBody);

resourceBehaviorOptions

resourceBehaviorOptions controls specific group behaviors at creation. WelcomeEmailDisabled simply stops Microsoft 365 from sending the welcome email to members.

You can also combine multiple options in the same list if needed:

{ "resourceBehaviorOptions", new List<string> { "WelcomeEmailDisabled", "HideGroupInOutlook" } }

Other supported values are documented here.

owners@odata.bind and members@odata.bind

The @odata.bind syntax binds users to the group by their full resource URL at creation time, so you don’t need separate POST /groups/{id}/members calls afterward. The URL format must be the full Graph v1.0 path:

https://graph.microsoft.com/v1.0/users/{objectId}

References

Jeppe Spanggaard

A passionate software developer. I love to build software that makes a difference!

Stop Spamming Your Users: Create Microsoft 365 Groups Without Welcome Emails