telnet to port 25 Not route to host

mfoley · 11-16-2023, 10:32 PM

I'm trying to send an email to host, but it's not going. I've tried 'telent host 25' and also port 587, but I get connection refused. 'telnet localhost 25' works. From a remote host I can telnet to various other ports on that host without problem. I've stopped the firewall and sendmail is running. /etc/mail/access is empty. According to netstat, sendmail is listening on both ports:

Code:

netstat -nlpl
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:25              0.0.0.0:*               LISTEN      21010/sendmail: acc 
tcp        0      0 0.0.0.0:587             0.0.0.0:*               LISTEN      21010/sendmail: acc

How can it be that sendmail is listening on 25/587, no firewall is running, and yet remote hosts can't connect to these ports?

Ser Olmy · 11-18-2023, 10:54 PM

Perhaps an ISP router is blocking the port(s), returning an ICMP "unreachable" error?

Running tcpdump (at the client end) should be sufficient to confirm whether this is the case or not.

JJJCR · 11-19-2023, 09:32 PM

Quote:

, but I get connection refused

refused would mean IP is block, or not allowed

have you tried asking whether remote party is doing IP Whitelisting?

If yes, then asked them to whitelist your IP. And check again.

bitfuzzy · 11-21-2023, 06:12 AM

Is your host name listed in /etc/mail/local-host-names ?

Is your host name listed in /etc/hosts (xxx.xxx.xx.xxx somedomain1.com somedomain1)?

If DNS is involved, have you verified the MX entry points to your domain / IP ?