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Can I use an additional port other than port 25 for SMTP connections? I was told I should open up one more ports for SMTP because most ISPs block port 25 now.

Article ID: 837, created on Oct 6, 2008, last review on Jul 7, 2014

  • Parallels Plesk for Linux/Unix
  • Parallels Plesk 12.0 for Windows
  • Parallels Plesk 10.1 for Windows


Can I use an additional port other than port 25 for SMTP connections? I was told I should open up more ports for SMTP because most ISPs block port 25 now.


(Parallels Plesk Panel 9.5.x - 11.x)

By default, Parallels Plesk Panel (Plesk) 11 accepts mail submission on TCP port 587.

Open Tools & Settings > Mail Server Settings (in the Mail group). Select the Enable message submission checkbox

We recommend that you use the Plesk web interface to configure the Postfix Submission port. If you configure the SMTP submission port directly in MTA, the setting can be overwritten by Plesk.

Follow the instructions below to configure an additional SMTP port for your MTA:

QMail (Parallels Plesk Panel 8.x, 9.x)

Choose any unused port and add it to the /etc/services file. For example:

  smtp_alt 25025/tcp # new SMTP port  

If you have 'xinetd' as a super-server, make a copy of /etc/xinetd.d/smtp_psa to /etc/xinetd.d/smtp_psa_alt and correct the service line within the new file:

service smtp_alt

Restart xinetd /etc/init.d/xinetd restart and the SMTP connections will be accepted on both the standard and 25025 ports. You may also need to reconfigure Horde IMP (webmail) settings so they use the alternative SMTP port. This can be done in the /etc/psa-horde/imp/servers.php file under the smtpport parameter for both IMAP and POP3 servers.

If you have a 'netd' super-server (Debian or FreeBSD), modify inetd.conf to enable an additional SMTP port:

grep '^smtp ' /etc/inetd.conf | sed 's/^smtp/smtp_alt/' >> /etc/inetd.conf

and restart inetd.

NOTE: If you want to disable the default (25) port completely and only use an alternate one, please do not block port 25 at the firewall and do not remove the smtp_psa service from the xinetd/inetd. Instead, set the default SMTP service to be listened only on by adding bind = to /etc/xinetd.d/smtp_psa. Otherwise, the SMTP service status will be displayed incorrectly in the Plesk control panel. Plesk determines SMTP service status by checking the 25th port and the port number is hardcoded there.

Postfix (Parallels Plesk Panel 9.x, 10.x, ...)

Add the following line to the Postfix configuration file /etc/postfix/

<IP_Address>:<port> inet n - n - - smtpd

where <IP_Address> is the IP address of your server and <port> is the additional port for the SMTP connection.

If Postfix is configured to use Postfix Before-Queue Content Filter extend the line with the proxy filter settings:

<IP_Address>:<port> inet n - - - - smtpd -o smtpd_proxy_filter=

Reload the mail service with mailmng after the reconfiguration:

# /usr/local/psa/admin/sbin/mailmng --reload-service
Reloading postfix: [  OK  ]

Search words:

Must issue a STARTTLS command first

port 25 is blocked

smtp server issue

not working 587 port


port 587


Message submission

smtp alternate port



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