Can't connect to port 25 from another system

[Alastair Neil]

Did you check hosts.allow and hosts.deny in /etc?


On 4/21/06, Debbie Deutsch <fedoralist at ddeutsch.org> wrote:
>
> Perhaps someone can help me with this problem.  I have sendmail running
> on an FC5 system.*  It works to the extent that I can send email from
> that system to other systems in other domains.  The problem is that
> other systems cannot initiate a connection to it.  Here are the key
> facts that I have been able to confirm:
>
>
> - I previously edited the sendmail.mc file to be sure it is listening on
> port 25 and did a make to update sendmail.cf.  Then I stopped and
> restarted sendmail.
>
> - Sendmail is definitely running.
>
> - Both netstat and nmap confirm that the system *is* listening on port
> 25, as it should be.
>
> - When I attempt to telnet to port 25 the connection fails. However,
> telnet definitely is running.  I can telnet to the host without
> specifying a port and successfully communicate with the telnet server.
> On the other hand, when I try to telnet to port 23 (where netstat and
> nmap confirm that the telnet server is listening), I get the same error
> as when I try to telnet to port 25.  I have tried this from multiple
> hosts on my LAN, all with the same results.
>
> - In an effort to rule out firewalls as a possible source of the
> problem, I disabled selinux completely and stopped iptables.  (I did not
> see anything in iptables that should block port 25 but I wanted to be
> sure it was not the source of the problem.)
>
> - All of the above testing was done on my LAN.  The traffic did not
> traverse my hardware router/firewall.  In any case, the firewall is
> configured to not block port 25.  (I had sendmail running successfully
> before, on an old system that finally went belly-up.)
>
> - As noted above, I can successfully send mail that requires sendmail to
> connect to another smtp server that is outside my LAN.
>
> All of this makes me think that there is some firewall-like thing going
> on where outbound smtp connections are okay but smtp sessions that are
> initiated by another host are not.  The behavior with telnet connections
> only working if the port is not specified baffles me.  With selinux and
> iptables turned off, I am out of ideas.  Any suggestions?
>
> TIA,
>
> Debbie
>
> *32-bit FC5 running on a 64-bit system because 54-bit FC5 installs but
> won't boot completely.  You may remember the recent thread...
>
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