To start, stop, or restart the Postfix mail server on a Linux or Unix system, you can use the systemctl command.
To start the Postfix mail server, use the following command:
sudo systemctl start postfix
To stop the Postfix mail server, use the following command:
sudo systemctl stop postfix
To restart the Postfix mail server, use the following command:
sudo systemctl restart postfix
Keep in mind that you will need to have root privileges to start, stop, or restart the Postfix mail server.
You can also use the systemctl command to check the status of the Postfix mail server. For example:
sudo systemctl status postfix
This will display the current status of the Postfix mail server, including whether it is running or stopped, and any error messages.
If you are using a different init system, such as systemv or upstart, you will need to use the appropriate commands for your system to start, stop, or restart the Postfix mail server.