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Windows Ninja
Asked: 2012-03-21 12:08:07 +0800 CST

Unable to Telnet into port 25 on CentOS PostFix Server

  • 772

I'm trying to telnet into port 25 on a CentOS server that runs PostFix to test sending email messages from the server.

When I try to telnet in from another CentOS box on the same network I get the message below:

 Unable to connect to remote host: Connection refused

SELinux is disabled and I've opened port 25 in iptables...what else should I be looking at?

networking

5 Answers

  1. Best Answer

    Run the following the check if postfix is listening on port 25/tcp:

    netstat -plnt |grep :25

    You should see a line like:

    tcp 0 0 0.0.0.0:25 0.0.0.0:* LISTEN 2460/master

    If you don't see such a line, check /etc/postfix/master.cf.

    In that file, you should see a line like:

    smtp      inet  n       -       n       -       -       smtpd

    The first column is the port, which postfix derives from /etc/services.

    You should look up general documentation on setting up Postfix, so your server doesn't become a spam relay. The CentOS wiki has fairly good documentation in that regard.

    Update:

    Also, look at http://www.postfix.org/postconf.5.html#inet_interfaces which will describe how to configure Postfix to listen on different network interfaces. The relevant line will be found in /etc/postfix/main.cf.

    • 15

  2. I edited the file /etc/postfix/main.cf. The parameter to look up was

    inet_interfaces = localhost

    I changed it to

    inet_interfaces = $myhostname, localhost

    Restart postfix. The problem was fixed.

    • 11

  3. I had this problem and found that I needed to do:

    # service postfix stop

    followed (a bit later) by

    # service postfix start

    Postfix reload did not seem to close and then re-open the required ports.

    • 3

  4. I generally only see the Connection Refused message if there is nothing listening. Are you sure you have an SMTP server running on the external IP address? Check with 

    netstat -tunlp | grep 25
tcp      0    0 127.0.0.1:25              0.0.0.0:*         LISTEN    1743/master

    Here you can see I'm only running on the loopback interface.

    • 2

  5. Check your /etc/hosts.allow and /etc/hosts.deny files. Maybe the telnet or the ports are blocked in those?!

    • 1