Adding a message to the checkout email
Since Zen Cart 1.5.6, the capability to add a static message to the order confirmation email has been built in. The file containing the message is located at ‘includes/languages/english/email_extras.php’. If you edit the file, save it as
includes/languages/english/YOURTEMPLATE/email_extras.php to add it to your template’s override. If the file already exists at ‘includes/languages/english/YOURTEMPLATE/email_extras.php’, then set the defined constant
EMAIL_ORDER_MESSAGE with your additional message and save the file.
There is also a notifier called
NOTIFY_ORDER_SET_ORDER_MESSAGE which fires when the message is being added, providing the opportunity for customization.
If your Zen Cart version is older than 1.5.6, you may use the Order Message plugin.
You can test your changes to the checkout email using the Test Checkout Email plugin.