SendMailPostRequestBody defaults SaveToSentItems to false in 6.2.0

Describe the bug

Microsoft.Graph 6.2.0 initializes SendMailPostRequestBody.SaveToSentItems to false.

As a result, applications that do not explicitly assign this optional property serialize "saveToSentItems": false.
Messages are delivered successfully but are not saved in the sender's Sent Items folder.

This conflicts with the Microsoft Graph sendMail API contract, which documents saveToSentItems as optional,
defaulting to true, and says it should be specified only when the desired value is false:

https://learn.microsoft.com/en-us/graph/api/user-sendmail?view=graph-rest-1.0

This behavior differs from Microsoft.Graph 5.104.0, where the generated request-body constructor leaves
SaveToSentItems unset (null) and therefore allows the service default to apply.

Expected behavior

Constructing a request body without explicitly assigning SaveToSentItems should omit the property from the
serialized request:

var requestBody = new SendMailPostRequestBody
{
    Message = message,
};

The service should consequently apply its documented default of true, and the sent message should appear in Sent
Items.

Alternatively, if the SDK assigns a client-side default, it should assign true, not false.

How to reproduce

Using Microsoft.Graph 6.2.0:

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

var message = new Message
{
    Subject = "Sent Items reproduction",
    Body = new ItemBody
    {
        ContentType = BodyType.Text,
        Content = "Test message",
    },
    ToRecipients =
    [
        new Recipient
        {
            EmailAddress = new EmailAddress
            {
                Address = "recipient@example.com",
            },
        },
    ],
};

var requestBody = new SendMailPostRequestBody
{
    Message = message,
};

await graphClient.Me.SendMail.PostAsync(requestBody);

Observe that:

1. The recipient receives the message.
2. The message is not present in the authenticated sender's Sent Items folder.
3. The request body serializes saveToSentItems as false.

The compiled 6.2.0 constructor contains the equivalent of:

SaveToSentItems = false;

The same constructor in Microsoft.Graph 5.104.0 does not initialize this property.

SDK Version

6.2.0

Latest version known to work for scenario above?

5.104.0

Known Workarounds

Explicitly assign SaveToSentItems = true:

var requestBody = new SendMailPostRequestBody
{
    Message = message,
    SaveToSentItems = true,
};

Debug output

Relevant constructor IL from Microsoft.Graph 6.2.0:

ldarg.0
ldc.i4.0
newobj System.Void System.Nullable<System.Boolean>::.ctor(!0)
call System.Void
Microsoft.Graph.Me.SendMail.SendMailPostRequestBody::set_SaveToSentItems(System.Nullable<System.Boolean>)

The generated serializer then writes the property:

call System.Nullable<System.Boolean> SendMailPostRequestBody::get_SaveToSentItems()
callvirt System.Void ISerializationWriter::WriteBoolValue(...)

In Microsoft.Graph 5.104.0, the constructor has no corresponding assignment to SaveToSentItems.

Configuration

• Microsoft.Graph 6.2.0
• Microsoft.Graph.Core 4.0.1
• Microsoft.Kiota.Abstractions 2.0.0
• Microsoft.Kiota.Serialization.Json 2.0.0
• .NET 10
• Windows
• Delegated authentication
• Endpoint: POST /me/sendMail

Other information

Microsoft.Graph 6.2.0's release notes mention “generation: update request builders and models,” so this appears to
have been introduced by the model-generation update:

https://github.com/microsoftgraph/msgraph-sdk-dotnet/releases/tag/6.2.0

The REST endpoint itself does not appear to be at fault. Omitting saveToSentItems in a direct REST request uses the
documented service default and saves the message in Sent Items.

Start with the generated SendMailPostRequestBody model and its constructor, then compare the 6.2.0 and 5.104.0 versions described in the issue. Verify serialization for an unset SaveToSentItems value and confirm that the request omits saveToSentItems so the /me/sendMail service default applies.