title: SSRS 2016 - Failure sending mail: The operation has timed out.Mail will not be resent
body: <p>I am constantly getting the following error when sending out email subscriptions (data driven)</p>
  
  <pre><code>   at Microsoft.ReportingServices.EmailDeliveryProvider.EmailProvider.Deliver(Notification notification)
  notification!WindowsService_5!2754!07/31/2018-10:12:22:: e ERROR: Error occurred processing subscription ec52efbe-63be-4b47-85e1-fa8f850d76ab: Failure sending mail: The operation has timed out.Mail will not be resent.
  notification!WindowsService_5!2754!07/31/2018-10:12:22:: i INFO: Notification 8290464c-90d6-4e58-859e-33f4a4e24a74 completed.  Success: False, Status: Failure sending mail: The operation has timed out.Mail will not be resent., DeliveryExtension: Report Server Email, Report: Invoice, Attempt 0
  emailextension!WindowsService_5!8c0!07/31/2018-10:12:33:: e ERROR: Error sending email. Exception: System.Net.Mail.SmtpException: The operation has timed out.
     at System.Net.Mail.SmtpClient.Send(MailMessage message)
  </code></pre>
  
  <p>I don't think it's the report timing out as it runs fine for file share subscription without any errors.. Only about 60 - 70 emails are generated at any one time and more than 75% fail with the above error.. yet I have the same report doing over 400 for file share and they all work fine. (0 errors)</p>
  
  <p>I've looked at report server settings and increased the session timeout value etc.. but hasn't made any difference.. </p>
  
  <p>I'm using SSRS 2016 (64 Bit) Enterprise on Windows Server 2012 R2 (64 bit)</p>
  
  <p>I can't seem to find any sort of definitive pointers online.. any help would be appreciated </p>