EWS The server cannot service this request right now - exchange-server

Question

I am seeing errors while exporting email in office 365 account using ews managed api, "The server cannot service this request right now. Try again later." Why is that error occurring and what can be done about it?
I am using the following code for that work:-
_GetEmail = (EmailMessage)item;
bool isread = _GetEmail.IsRead;
sub = _GetEmail.Subject;
fold = folder.DisplayName;
historicalDate = _GetEmail.DateTimeSent.Subtract(folder.Service.TimeZone.GetUtcOffset(_GetEmail.DateTimeSent));
props = new PropertySet(EmailMessageSchema.MimeContent);
var email = EmailMessage.Bind(_source, item.Id, props);
bytes = new byte[email.MimeContent.Content.Length];
fs = new MemoryStream(bytes, 0, email.MimeContent.Content.Length, true);
fs.Write(email.MimeContent.Content, 0, email.MimeContent.Content.Length);
Demail = new EmailMessage(_destination);
Demail.MimeContent = new MimeContent("UTF-8", bytes);
// 'SetExtendedProperty' used to maintain historical date of items
Demail.SetExtendedProperty(new ExtendedPropertyDefinition(57, MapiPropertyType.SystemTime), historicalDate);
// PR_MESSAGE_DELIVERY_TIME
Demail.SetExtendedProperty(new ExtendedPropertyDefinition(3590, MapiPropertyType.SystemTime), historicalDate);
if (isread == false)
{
Demail.IsRead = isread;
}
if (_source.RequestedServerVersion == flagVersion && _destination.RequestedServerVersion == flagVersion)
{
Demail.Flag = _GetEmail.Flag;
}
_lstdestmail.Add(Demail);
_objtask = new TaskStatu();
_objtask.TaskId = _taskid;
_objtask.SubTaskId = subtaskid;
_objtask.FolderId = Convert.ToInt64(folderId);
_objtask.SourceItemId = Convert.ToString(_GetEmail.InternetMessageId.ToString());
_objtask.DestinationEmail = Convert.ToString(_fromEmail);
_objtask.CreatedOn = DateTime.UtcNow;
_objtask.IsSubFolder = false;
_objtask.FolderName = fold;
_objdbcontext.TaskStatus.Add(_objtask);
try
{
if (counter == countGroup)
{
Demails = new EmailMessage(_destination);
Demails.Service.CreateItems(_lstdestmail, _destinationFolder.Id, MessageDisposition.SaveOnly, SendInvitationsMode.SendToNone);
_objdbcontext.SaveChanges();
counter = 0;
_lstdestmail.Clear();
}
}
catch (Exception ex)
{
ClouldErrorLog.CreateError(_taskid, subtaskid, ex.Message + GetLineNumber(ex, _taskid, subtaskid), CreateInnerException(sub, fold, historicalDate));
counter = 0;
_lstdestmail.Clear();
continue;
}
This error occurs only if try to export in office 365 accounts and works fine in case of outlook 2010, 2013, 2016 etc..

Answer 1

Usually this is the case when exceed the EWS throttling in Exchange. It is explain in here.
Make sure you already knew throttling policies and your code comply with them.
You can find throttling policies using Get-ThrottlingPolicy if you have the server.

Answer 2

One way to solve the throttling issue you are experiencing is to implement paging instead of requesting all items in one go. You can refer to this link.
For instance:
using Microsoft.Exchange.WebServices.Data;
static void PageSearchItems(ExchangeService service, WellKnownFolderName folder)
{
int pageSize = 5;
int offset = 0;
// Request one more item than your actual pageSize.
// This will be used to detect a change to the result
// set while paging.
ItemView view = new ItemView(pageSize + 1, offset);
view.PropertySet = new PropertySet(ItemSchema.Subject);
view.OrderBy.Add(ItemSchema.DateTimeReceived, SortDirection.Descending);
view.Traversal = ItemTraversal.Shallow;
bool moreItems = true;
ItemId anchorId = null;
while (moreItems)
{
try
{
FindItemsResults<Item> results = service.FindItems(folder, view);
moreItems = results.MoreAvailable;
if (moreItems && anchorId != null)
{
// Check the first result to make sure it matches
// the last result (anchor) from the previous page.
// If it doesn't, that means that something was added
// or deleted since you started the search.
if (results.Items.First<Item>().Id != anchorId)
{
Console.WriteLine("The collection has changed while paging. Some results may be missed.");
}
}
if (moreItems)
view.Offset += pageSize;
anchorId = results.Items.Last<Item>().Id;
// Because you’re including an additional item on the end of your results
// as an anchor, you don't want to display it.
// Set the number to loop as the smaller value between
// the number of items in the collection and the page size.
int displayCount = results.Items.Count > pageSize ? pageSize : results.Items.Count;
for (int i = 0; i < displayCount; i++)
{
Item item = results.Items[i];
Console.WriteLine("Subject: {0}", item.Subject);
Console.WriteLine("Id: {0}\n", item.Id.ToString());
}
}
catch (Exception ex)
{
Console.WriteLine("Exception while paging results: {0}", ex.Message);
}
}
}