"Could not reach Exchange SMTP server — check that IP port 25 is not blocked"

POPcon cannot connect to Exchange on port 25. Troubleshooting steps:

1. Check the POPcon log file — it shows the IP address it is trying to reach. Verify this is the correct Exchange server address.
2. In Exchange, verify the receive connector's Network tab includes the POPcon server's IP in the allowed addresses.
3. Confirm the Microsoft Exchange Transport service is running on the Exchange server.
4. Test connectivity: telnet exchangeservername 25. You should see a 220 ... banner.
5. If the telnet fails, port 25 is blocked — check the Windows firewall and any network firewall between the two machines.