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How to configure alternate SMTP port OR change the SMTP port on a Plesk server?

Sometimes some ISPs block port 25 for security reasons in which case, you need to open an alternate SMTP port on your server for your clients. Plesk do not offer a straight forward method of configuring an alternate SMTP port, instead you have to configure it manually.

SMTP on Plesk servers runs under xinetd service and the location of the file is /etc/xinetd.d/smtp_psa.

In order to configure an alternate port say for example 2525, follow the below steps:

1. Make a copy of file “smtp_psa” under the /etc/xinetd.d/ directory

# cp -p smtp_psa smtp_psa_new

2. Edit the smtp_psa_new file and replace the line

service smtp
with
service smtp_new

3. You now need to edit the /etc/services file and make sure the lines with port 2525 should look as follows:

smtp_new      2525/tcp      #alternate SMTP port
smtp_new      2525/udp      #alternate SMTP port

4. Save the file and restart the xinetd service.

# /etc/init.d/xinetd restart

SMTP service will now listen on port 2525 as well which you can verify using the ‘telnet’ command:

# telnet yourserverip 2525