Microsoft Graph API using uploadsession not able to recieve email with attachments - microsoft-graph-api

Question

Email Not been recieved with attachments when I try to use Uploadsession using Graph API. can someone help me uderstand why this is happening. I have not recieved any error.
Message draft = await graphServiceClient.Users["UserID"].Messages.Request().AddAsync(email);
//Message draft = graphServiceClient.Users["UserID"].Mailfolders.Drafts.Messages.Request().AddAsync(email);
var stream = System.IO.File.Open(#"C:\attach\DYN28_6579332_33242556.csv", System.IO.FileMode.Open, FileAccess.Read, FileShare.None);
var attachmentItem = new AttachmentItem
{
AttachmentType = AttachmentType.File,
Name = "DYN28_6579332_33242556.csv",
Size = stream.Length
};
var uploadSession = await graphServiceClient.Users["Userid"].Messages[draft.Id]
.Attachments
.CreateUploadSession(attachmentItem)
.Request()
.PostAsync();
var maxSlicesize = 320 * 1024;
var largeFileUploadTask = new LargeFileUploadTask<FileAttachment>(uploadSession, stream, maxSlicesize);
IProgress<long> progress = new Progress<long>(prog => {
Console.WriteLine($"Uploaded {prog} bytes of {stream.Length} bytes");
});
// Upload the file
var uploadResult = await largeFileUploadTask.UploadAsync(progress);
if (uploadResult.UploadSucceeded)
{
// The ItemResponse object in the result represents the
// created item.
//Console.WriteLine($"Upload complete, item ID: {uploadResult.ItemResponse.Id}");
Console.WriteLine("upload completed");
}
Finally sending email with
await graphServiceClient.Users["userid"].Messages[draft.Id]
.Send()
.Request()
.PostAsync();

Answer 1

There is a limit of 4MB on a single request in the Graph API. To send larger attachments, you need to first create an upload session against the email message/calendar event, and upload your attachment in a number of requests as part of this session. AFAIK each of the smaller POST requests would also need to stay below the 4MB limit.
You can find more detailed documentation and a sample walkthrough here.
POST https://graph.microsoft.com/v1.0/me/messages/AAMkADI5MAAIT3drCAAA=/attachments/createUploadSession
Content-type: application/json
{
"AttachmentItem": {
"attachmentType": "file",
"name": "flower",
"size": 3483322
}
}