Hello Technet forum
                                                                

we use Exchange 2007 SP1                                        
Users use exclusive OWA to access their mailboxes.               
Based on the fact that via OWA  is not possible to set folder rights    
(example: calendar Read; Mailbox: Editor) were trying to use EWS to set this rights.  
EWS does not support groups. Based on this EWS is used to add all the users one by one 
by the AddDelegate API for example .
                                                                          
                                                                         
                                                                         
We found out that only 219 users can be set on a folder via    
EWS, for example only 219 users can be set on the calendar of one user   
with read permissions.
We need to add up to at least 300 users to have read access
After 219 users it is not possible to add any further users.

The EWS log shows:

2013-07-23 07:39:12 DEBUG - EwsDelegation$RequestContext.(68) - Create RequestContext with parameters(https://xxxxxxx.xxx.xxx/ews/Exchange.asmx,pad01,econews,**passwd**,user@xxxxxx.xxx,user2@xxxx.xxx,false)
2013-07-23 07:39:29 ERROR - EwsDelegation.checkOperationResult(714) - AddDelegate [mailbox=user@xxxxxx.xxx delegateUser=user2@xxxx.xxx] [permissions: Calendar.REVIEWER,Contacts.NONE,Inbox.NONE] :: Failed! Reason: ErrorAddDelegatesFailed Failed to add one or more delegates.
                                      
This only happens starting from the 219th user we're adding                                                                         
                                                                         
Is there any hard limitation in the EWS interface or in Exchange about   
the number of users which can be set via this functionality?   

Moreover we noticed also the first requests were completed in about one second per user , then they started to be performed in 10 seconds per user , until they degrades to 30 seconds per user until they stop with the error above at the user number 219.

We can't also explain this apparent performance degradation.

Any help will be very appreciated

Anyone can help me on this?

Many thanks

Gianluca