SendMail ignores extended MAPI properties specified as SingleValueExtendedProperties

[obartelt]

When sending a mail with SendMail.PostAsync, extended MAPI properties specified in Message.SingleValueExtendedProperties are ignored or at least not appearing in the mail received by the recipient. In this case, the Return-Path header was added using the following snippet, because adding it as an InternetMessageHeader is not allowed, and sending the mail in MIME format with the header doesn't work either:

message.SingleValueExtendedProperties.Add(new Microsoft.Graph.Models.SingleValueLegacyExtendedProperty
{
    Id = "String 0x1046",  // PidTagInternetReturnPath
    Value = email.ReturnPath.EmailAddress
});

Expected behavior: set the Return-Path header in the sent mail to the specified address.
Version: Microsoft Graph 5.34.0, .NET Standard 2.0 with .NET 6.0 test application

[andrueastman]

Thanks for raising this @obartelt

As this this is a question related to the behaviour of the API and this repo is mainly intended for issued related to the function of SDK, any chance you can post a question at the link below to get guidance from the API owners on whether sending an email in mime format allows the addition of SingleValueExtendedProperties as well? It would be great if you could post back the link as a comment so that anyone else with the question may also be able to discover it.

https://learn.microsoft.com/en-us/answers/tags/161/ms-graph

[microsoft-github-policy-service]

This issue has been automatically marked as stale because it has been marked as requiring author feedback but has not had any activity for 4 days. It will be closed if no further activity occurs within 3 days of this comment.