Postfix-Server behind a DSL-Router

[Peter Ulrich Kruppa]

Am 09.04.2015 um 13:20 schrieb Frank Elsner:
> On Thu, 9 Apr 2015 12:47:15 +0200 Peter Ulrich Kruppa wrote:
>
>    [ ... ]
>
>>        Yes: when I use telnet on port 25 from my Fedora I get
>>           # telnet localhost 25
>>          Trying ::1...
>>          telnet: connect to address ::1: Connection refused
>>          Trying 127.0.0.1...
>>          Connected to localhost.
>>          Escape character is '^]'.
>>          220 pukruppa.de ESMTP
>
> Ok, let's test.
>
> # host -t mx pukruppa.de
> pukruppa.de mail is handled by 10 mail.pukruppa.de.
> # telnet mail.pukruppa.de 25
> Trying 217.92.171.227...
> telnet: connect to address 217.92.171.227: Connection timed out
>
> There is no SMTP daemon listening for the outside world.
> I guess the missing port forwarding ist the problem.
I enabled port forwarding for port 25 in my router - though of course
one never knows, what it really does ...

I guess, it must be a bit more tricky. I just sent myself a mail from
googlemail listening on my Fedora box with:

	# tcpdump -n -i any tcp port 25
and instantly receive a lot of activity like
[...]
13:33:56.106134 IP 209.85.212.178.35510 > 192.168.10.1.smtp: Flags [S], 
seq 1810379351, win 42900, options [mss 1418,sackOK,TS val 987921454 ecr 
0,nop,wscale 7], length 0
13:33:58.105979 IP 209.85.212.178.35510 > 192.168.10.1.smtp: Flags [S], 
seq 1810379351, win 42900, options [mss 1418,sackOK,TS val 987923454 ecr 
0,nop,wscale 7], length 0
[...]	

And 209.85.212.178 seems to be some google machine.

To me this looks as if port forwarding is all-right but Postfix does not 
react (?!?)


Peter


>
>
> --Frank
> .
>