POPcon downloads email fine but cannot reach my Exchange server

POPcon successfully downloads from your POP3/IMAP server but fails to deliver to Exchange via SMTP. Troubleshooting steps:

1. Verify the Exchange server address — use the server's network name (e.g. exchangeserver), not the internet domain.
2. Verify Exchange services are running — check that "Microsoft Exchange Transport" service is started.
3. Test with PING — run ping exchangeserver from the POPcon machine to confirm network connectivity.
4. Test SMTP port 25 — run telnet exchangeserver 25. You should see an SMTP banner. If not, port 25 is blocked.
5. Check firewall rules — ensure port 25 is open between the POPcon machine and Exchange.
6. Check antivirus / antispam — some endpoint security products intercept or block outbound SMTP. Try disabling temporarily to test.
7. Check the receive connector — verify the POPcon machine's IP address is allowed to connect (see Exchange receive connector settings).

The complete setup from accepted domain to first test, including the receive connector settings this article refers to, is in the guide How to download POP3 and IMAP mailboxes into Exchange 2016, 2019 and SE. Which of these checks matter at which placement of the connector — on the Exchange server, a member server or a workstation — is in Where to install a POP3/IMAP connector.