Internal Server Error while sending mail with extended property

Question

I am using EWS Managed API. I just started fiddling with Extended properties. So I wrote simple code to send a simple mail with extended property attached to it.
Forming the mail part I simply copy pasted from this
MSDN page. For testing purpose I suppressed certificate validations.
This is my complete code:
1 ServicePointManager.ServerCertificateValidationCallback = delegate(object s, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors) { return true; };
2 service = new ExchangeService(ExchangeVersion.Exchange2007_SP1);
3 service.TraceListener = new TraceListener();
4 service.TraceEnabled = false;
5
6 service.Credentials = new WebCredentials("[email protected]", "password@123");
7 service.Url = new Uri("https://exchng.domain.com/EWS/Exchange.asmx");
8
9 Guid MyPropertySetId = new Guid("{C11FF724-AA03-4555-9952-8FA248A11C3E}");
10
11 // Create a definition for the extended property.
12 ExtendedPropertyDefinition extendedPropertyDefinition = new ExtendedPropertyDefinition(MyPropertySetId, "Expiration Date", MapiPropertyType.String);
13
14 // Create an e-mail message that you will add the extended property to.
15 EmailMessage message = new EmailMessage(service);
16 message.Subject = "Saved with extendedPropertyDefinition of two days";
17 message.Body = "The expiration date is contained within the extended property.";
18 message.ToRecipients.Add("[email protected]");
19
20 // Add the extended property to an e-mail message object named "message".
21 message.SetExtendedProperty(extendedPropertyDefinition, DateTime.Now.AddDays(2).ToString());
22
23 // Save the e-mail message.
24 message.SendAndSaveCopy();
Please find the rest of the question in first reply, as I got "Body must be 4 to 60000 characters long".

Answer 1

Rest of the question:
I am getting below exception (with no nested inner exceptions) on line 24:
An internal server error occurred. The operation failed.
at Microsoft.Exchange.WebServices.Data.ServiceResponse.InternalThrowIfNecessary()
at Microsoft.Exchange.WebServices.Data.ServiceResponse.ThrowIfNecessary()
at Microsoft.Exchange.WebServices.Data.MultiResponseServiceRequest`1.Execute()
at Microsoft.Exchange.WebServices.Data.ExchangeService.InternalCreateItems(IEnumerable`1 items, FolderId parentFolderId, Nullable`1 messageDisposition, Nullable`1 sendInvitationsMode, ServiceErrorHandling errorHandling)
at Microsoft.Exchange.WebServices.Data.ExchangeService.CreateItem(Item item, FolderId parentFolderId, Nullable`1 messageDisposition, Nullable`1 sendInvitationsMode)
at Microsoft.Exchange.WebServices.Data.Item.InternalCreate(FolderId parentFolderId, Nullable`1 messageDisposition, Nullable`1 sendInvitationsMode)
at Microsoft.Exchange.WebServices.Data.EmailMessage.InternalSend(FolderId parentFolderId, MessageDisposition messageDisposition)
at Microsoft.Exchange.WebServices.Data.EmailMessage.SendAndSaveCopy()
If I comment line number 21, the code works fine and sends the message. So why it fails with extended properties?