When performing mailbox operations via Exchange Web Services (EWS), you may encounter the error:
"The server cannot service the request".
This typically occurs due to throttling or temporary unavailability of the Exchange service (Office 365 or on-premises).

Cause

  • EWS Throttling: Office 365 or Exchange on-premises limits the number of concurrent requests per user or application to maintain service performance.
  • Temporary Service Unavailability: The Exchange server may be busy, undergoing maintenance, or experiencing a temporary outage.

Resolution

  1. Wait and Retry:
    • Wait a few minutes before trying again. Throttling limits are reset periodically.
  2. Reduce Request Load:
    • Schedule mailbox operations in batches rather than running all at once.
  3. Check Service Health:
  4. If Persistent:
    • For on-prem Exchange, consult your Exchange admin to review throttling policies.

Additional Notes

  • This is not typically a permanent issue—most cases resolve automatically once throttling limits reset.
  • If you frequently encounter throttling, consider implementing EWS client throttling best practices or request an adjustment to throttling policies from your Exchange admin.