I have the problem that I cannot connect to my exim4 SMTP server from my home network:
$ telnet -4 example.com 25
Trying 1.2.3.4...
telnet: connect to address 1.2.3.4: Connection refused
telnet: Unable to connect to remote host
netstat
on the server tells me that exim4 is listening on port 25, both IPv4 and IPv6. I started tcpdump
on my server to check whether the request reaches the server, it shows nothing. I was puzzled and, as a last test, deleted all iptables
rules as described here. Still, I am getting the Connection refused error.
Wireshark tells me that the server responds to my telnet request with RST/ACK, which implies that the port is closed. However, if I connect to the server from anywhere but my home network, it works without problems.
I have checked that the request leaves my local gateway and it does.
So now I am out of ideas. What could possibly lead to this request being rejected? Since tcpdump
does not show anything and I get a RST/ACK, it must be at a very low level, but I cannot imagine what beyond iptables could block the incoming request – especially since this only seems to occur for packages from my home IP.