Symptoms
Some ISPs (Internet Service Providers) can block outgoing SMTP connections on known ports (25, 587, 2525) and users require to open one extra port for the SMTP service.
Resolution
On a POA-managed qmail hosting platform the SMTP service is invoked by the xinetd super-server each time when a user connects to the server.
To add one more available port (e.g. 1024), one can create the /etc/xinetd.d/smtp1024 file on a qmail server with the following content:
service smtp1024
{
type = UNLISTED
disable = no
port = 1024
socket_type = stream
protocol = tcp
wait = no
user = qmaild
group = qmail
server = /usr/local/qmail/bin/tcp-env
server_args = /usr/local/qmail/bin/qmail-smtpd /usr/local/qmail/bin/cmd5checkpw
cps = 0 0
}
and restart the xinetd service:
# service xinetd restart
After that it is possible to test the port using the telnet utility:
$ telnet localhost 1024
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 mail.example.com ESMTP
The server responds with SMTP greetings, so it is configured to serve connections on the port 1024.