Originally Posted by
cearlp2
I can send and receive data on the ubuntu 18.04 machine. I guess the indicates iPv4 works.
What exactly tests IPv4?
Which protocols are working and from where? Some simple network troubleshooting steps:
https://blog.jdpfu.com/2013/03/01/li...101-networking
It looks like DNS is working at some level.
The SMTP doesn't appear to work based on the logs and it also seems IPv6 is prioritized over IPv4. If only SMTP isn't working, that could mean the ISP is blocking outbound 25/tcp, which is common. ISPs do that to prevent spam on their networks. If the connection is residential, then you'll need to use the ISP's relay. There's 1 line in one of the postfix config files that's needed. In the main.cf for postfix, modify or add:
Code:
relayhost = {put ISP relay IP here.}
Check that file with postconf -n to see what options are actually being uses. If you need specific relays for different target email domains, there's a transport_custom file available.
If it is a business connection, probably just need to call the support line and get outbound SMTP opened for your static IP. If you don't have a static IP, it is likely that nobody will accept email, so just use the ISP's SMTP relay.
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