This Event ID 4019 from MSExchange ADAccess on your Exchange Server 2019 means the Exchange Control Panel (ECP) application pool (w3wp.exe) failed to receive an AD topology invalidation message through its internal RPC/notification port (9050). The specific error:

"A blocking operation was interrupted by a call to WSACancelBlockingCall"

...is a classic Winsock error indicating that a socket operation was forcefully stopped-usually by the system or another thread-perhaps during shutdown, recycling, or network interruption.

What It Usually Means

• Transient internal comms issue within the Exchange service stack, especially around AD topology notifications.
• The w3wp.exe (ECP) worker process was waiting on a socket and the call was canceled - often seen during IIS App Pool recycle, Exchange service restarts, or network latency.
• It doesn't mean AD is broken - but it could slow down ECP responsiveness or config updates if frequent.

Contextual Breakdown

• Port 9050 is used by Exchange for internal notification between components and services, including AD topology updates.
• The WSACancelBlockingCall error happens when a blocking call like select() or recv() is canceled-could be by another thread or shutdown logic.
• This is generally benign unless you're seeing it repeatedly (several times per minute or hour).

If This Happened Once or Rarely:

No action needed.

If This is Repeating Often:

Then you're looking at a deeper comms or service state issue. In that case:

1. Check for App Pool or Service Restarts

• Look at the System and Application logs for signs of:

  • IIS App Pool recycling (w3wp.exe)
  • Exchange AD Topology service restarts
  • Network hiccups

2. Check Event IDs 2080 or 1006

• These give more detail on Exchange's AD connectivity health.

3. Check Network

• DNS resolution delays
• Network latency to DCs
• NIC driver updates / teaming issues

4. Run Exchange Health Checks

Test-ServiceHealth
Get-EventLogLevel -Identity "MSExchange ADAccess"

5. Restart ECP app pool manually (if misbehaving)

Restart-WebAppPool MSExchangeECPAppPool

6. Review Exchange performance counters for ADAccess

Long-Term Suggestions

If this is plaguing you regularly:

• Consider increasing App Pool idle timeout or disabling rapid cycling in IIS.
• Monitor DC latency using:

Test-ReplicationHealth

• Ensure no firewall is filtering ephemeral ports or internal RPC between Exchange and DCs.

Bottom Line

This specific 4019 is typically not critical-just a hiccup in Exchange's internal AD comms-unless it's part of a pattern. If so, it's worth digging into IIS, Exchange services, and DC health for subtle instability.

Let me know if it's happening frequently and I'll help dig deeper.