How to send email from any one email using Microsoft Graph

Please note that since Graph API v. 5.0 (march 2023), Microsoft introduced an annoying breaking change, not really well documented (besides obscurely here).

Now, SendMail cannot be used anymore as a method of a User. You will get a CS1955 Non-invocable member cannot be used like a method compiler error if you try to do that.

You will have to do something like this:

        // Your old Message object definition
        Microsoft.Graph.Models.Message msg = new()
        {
            From = ...,
            ToRecipients = ...,
            Subject = "...",

            Body = new ItemBody
            {
                ContentType = BodyType.Html,
                Content = "..."
            }
        };

        Microsoft.Graph.Users.Item.SendMail.SendMailPostRequestBody body = new()
        {
            Message = msg,
            SaveToSentItems = false  // or true, as you want
        };

        try
        {
            await graphClient.Users["your user GUID"]
            .SendMail
            .PostAsync(body);
        }
        catch (Exception ex)
        {
            // log your exception here
        }