Postfix-Server behind a DSL-Router

[Peter Ulrich Kruppa]

Hi everyone,

please do excuse my unspecific subject - I don't really know what my
problem is yet.

I set up a Postfix-Server on my Fedora 21 box, which is connected to
the internet via
some Netgear Router. My private LAN is 192.168.10.0/24 with the Fedora
box fixed on
192.168.10.1 . My Netgear thing has got a fixed IP and hostname, let's say for
mydomain.com .

Now I can
  - send myself mails from my Fedora box
  - send mails from my Fedora box to the outside p. ex. my googlemail account

but I can't receive mails from outside.

When I do a
    # tcpdump -n -i any tcp port 25
on my Fedora I can see many messsages like

10:34:09.338691 IP 212.227.17.11.64945 > 192.168.10.1.smtp: Flags [S],
seq 3273717964, win 14600, options [mss 1418,sackOK,TS val 1273019143
ecr 0,nop,wscale 9], length 0
10:34:10.339378 IP 212.227.17.11.64945 > 192.168.10.1.smtp: Flags [S],
seq 3273717964, win 14600, options [mss 1418,sackOK,TS val 1273019393
ecr 0,nop,wscale 9], length 0
[...]

Any good ideas, what else I can do to analyze my problem?

Thanks for your answers

Peter