SMTP port 587 giving issues

[tneo]

I just migrated to OPNSense and have NordVPN configured on the router following the steps as given here: https://support.nordvpn.com/Connectivity/Router/1292598142/OPNsense-19-1-setup-with-NordVPN.htm

That all works, but for some reason I'm not able to send e-mail over port 587. When I want to send an e-mail over port 587 I get time-out errors. I can save the e-mail in the queue for later and the e-mail is shown, when I access my e-mail through a browser.

I'm able to connect just fine to retrieve and to write back to the server, it is only the sending that fails.

From a remote machine I can connect through openssl without problems. With my desktop that fails as well, thus I suspect opnsense blocking something for me.

Where can I poke to see what the issue is?

[meyergru]

I think NordVPN might block ports 25 and 587 in order not to get blacklisted because their customers send spam via their VPN infrastructure. ProtonVPN does this, for sure.

[tneo]

I have it resolved.

• I went over the NordVPN configuration again and identified 1 error.
• Disabled the IPv6 interface in OPNSense

I think the main cause was a conflict for IPv6, as I noticed that the server-name did not resolve and in the log the IPv6 showed up. Openssl into the IP of my server worked fine. And the NordVPN connection wants IPv4 only. So it's working. 8)