title: ExchangeService.FindItems()
body: <p>I've been requested to create an application that should create a common base from 3 different email addresses sources and update each base taking the most common updated dataset. 
  Among the three sources I have an Exchange server Contacts addressbook. I know that I can access such data trough EWS and in specific I should probably use the ExchangeService.FindPeople() method or maybe FindPersona().
  This should work but, since I'm looking only for new/updated contacts, it will load significantly the server (maybe not for new records but I cannot understand how to retrieve update records) and this it's not a good practice.
  I've found in MSDN docs a way to be notified on updates on message base but there's nothin related on updates on contacts:</p>
  
  <p><a href="https://msdn.microsoft.com/en-us/library/office/dn458791(v=exchg.150).aspx" rel="nofollow noreferrer">https://msdn.microsoft.com/en-us/library/office/dn458791(v=exchg.150).aspx</a></p>
  
  <p>Is there something to be notified on updates on contacts (even trough third party products/APIs).</p>
  
  <p>P.S. I would like to code in C# (or other .NET languages) but I'm open to anything else.</p>