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→Edit/Modify /etc/mail/sendmail.cf
tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN
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== Open SMTP port on the firewall ==
Run the following command:
/sbin/iptables -I INPUT -p tcp --dport 25 -j ACCEPT
Note that you can make the rule more restrictive by specifying the Source Network or IP address.
== Test the SMTP port locally ==
telnet localhost 25
== Test the SMTP port remotely ==
Login to another VMs and run the following command to connect to port 25 on 10.0.117.10
telnet 10.0.117.10 25
