SMTP on alternative port

If your ISP blocks port 25 connections to mail servers other than there own then you can configure the mail servers to listen on alternative port(s).

Here are the steps if you want smtp to listen on port 2525 as well as the standard port 25 and 465:

1. You need to add port 2525 to the /etc/services file:
   

   vi /etc/services

   Add the folowing line:

   smtp_alt 2525/tcp # new SMTP port

   Exit out of vi saving the file.

2. Make a copy of /etc/xinetd.d/smtp_psa to /etc/xinetd.d/smtp_psa_alt
   

   cp /etc/xinetd.d/smtp_psa /etc/xinetd.d/smtp_psa_alt

3. Change the Service line at top of the file:
   

   vi /etc/xinetd.d/smtp_psa_alt

   You should see

   service smtp

   It needs to be

   service smtp_alt

   Exit out of vi saving the file.

4. Restart the xinetd service
   

   /etc/init.d/xinetd restart

   or
   

   service xinetd restart

5. You then need to edit the plesk firewall (If it is enabled), you need to edit the current SMTP rule and add in the new port 2525

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