I'm building my skills for a future Tier 1 or Tier 2 IT support role and have been practicing networking, ticketing systems, Microsoft 365 administration, Active Directory, and Group Policy. For my lab, I created a simulated company with two branches, five departments per branch, and several user and computer GPOs.
I recently started setting up hMailServer as a free, self-hosted mail server on Windows. I created two accounts, [email protected] and [email protected], and I'm trying to send messages between them. I configured IMAP on port 143 for incoming mail and SMTP on port 25 for outgoing mail, but sending a message produces an error.
I'm still learning how the IP ranges, listeners, firewall rules, and mail protocols fit together. What should I check first, and is there another free mail-server application that would be easier or more suitable for a home lab?
5 Answers
Start by testing whether the SMTP service is actually reachable. From PowerShell on another machine, run `Test-NetConnection -ComputerName 192.168.56.10 -Port 25`. If it fails, check that hMailServer is listening on the expected interface and port, confirm the IP address, and allow TCP 25 through the Windows Firewall. On the mail-server machine, `netstat -ano` can show whether a program is listening on port 25. You can also use Wireshark or similar tools to see whether the connection attempt is leaving the client and receiving a response.
hMailServer is still useful for learning the basics of Windows mail administration, but it is old and not the easiest option for a new deployment. MailEnable has a free Windows edition, while Mailcow or Mail-in-a-Box can be good Linux-based lab projects if you have enough resources. Those alternatives are more complicated, though, so troubleshooting the current setup may teach you more about listeners, DNS, authentication, firewall rules, and SMTP than switching immediately.
IMAP on port 143 is only for retrieving mail; it does not send messages. SMTP on port 25 handles server-to-server delivery, but a mail client normally submits mail through an authenticated SMTP service, often on port 587 with STARTTLS. For a basic internal lab, port 25 can work, but the server must have a listener configured for the correct interface, and the client must use the hMailServer account credentials. Also make sure both users and the domain exist in hMailServer exactly as configured.
Using a `.local` domain is fine for experimenting with internal delivery, but it is not a publicly routable email domain. Messages addressed to external services will not work normally because public DNS and mail systems do not recognize that domain. For an isolated lab, keep both accounts on the same hMailServer and first test local delivery before attempting outside mail.
Check the IP ranges in hMailServer carefully. If the SMTP range is restricted to localhost, clients on another lab machine will not be allowed to connect. Add the correct private network range, such as your lab subnet, and configure authentication and relay permissions conservatively. Do not allow unrestricted relaying, even in a test environment.
That makes sense. I had been looking at the localhost settings and didn’t realize they would prevent another machine on the lab network from connecting. I’ll verify the subnet and test again.