Port 25 Connection Refused at Local IP

[t3dc]

Ok, I know... ISPs block port 25 -- however, I'm on a business plan and mine does not. Further, port 25 is responding with "Connection Refused" on my internal LAN and the Stalwart server itself -- so even if the ISP, or my WAN Firewall were blocking it, I should be able to reach it locally.

So I'm testing on the Stalwart box (which is an LXC on Proxmox) at the console:

telnet 192.168.xxx.xxx 25
Trying 192.168.xxx.xxx...
telnet: Unable to connect to remote host: Connection refused

telnet localhost 25
Trying ::1...
Connected to localhost.
Escape character is '^]'.
220 Stalwart.localdomain ESMTP Postfix (Debian/GNU)

I thought maybe it's not binding to the IP properly, so I rebuild the listener with the IP explicitly stated. Same result. So I reset it back to the initial state:

Here's the kicker. This all worked until Sept 4 (three days ago). I had an electrician out for service and had to turn the server off for several hours. When I restarted, suddenly port 25 was refusing connections.

HELP! I'm losing my mind.

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For clarity, here are the possible issues I have eliminated:

ISP Blocking Port 25 - The ISP block wouldn't affect my local LAN.

Router Firewall Blocking Port 25 - Again would not affect my local LAN.

Local Firewall on Stalwart Server - As mentioned above, it's an LXC. It has no firewall. Further the Proxmox host also has no firewall:

# iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination         

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination   

Other Connectivity Issues - I'm testing on the Stalwart LXC. However, I can also test from machines on a different continent. Port 587 responds instantly with the Stalwart Banner.

Blocked IPs - I have searched Stalwart's blocked IPs. Nothing from my LAN network is in the list, and I've explicitly allowed my LAN network on the Allowed IPs page.

Check the Logs - The logs show no traffic at all for the smtp listener. I see submission, imap, http, etc, but nothing happening on smtp, even when I tail the logs during a connect attempt. Strangely enough, this is true even for a successful connection to the loopback address as above.

[t3dc]

After a third reboot, the server is working properly again. I can't come up with an explanation why that is, but am relieved to have service.