re; Adding email advice, after a customer makes a purchase

What's the best file to edit to add extra email information, after a customer makes a purchase ? I can see the email folder with all the html templates. I'm wondering if it might be email_template_checkout.html or email_template_order_status.html

The question then becomes, how do I add extra customer advice to the html template. i.e. where exactly do I put it ? Is there a structure I have to follow or a special variable in a PHP file I can add extra info to, that is then referred to in the html email template ? or do I hard code it in the html email template ?

"email advice"? Do you mean tips on how to use email?

Of course you don't, but it's not clear what or why you want to add "advice" someplace.
What do you want to say, and why? What's the business reason for this?
And are you using HTML-formatted emails, or text-only?

Just using whatever the standard ZenCart email setup is. I just want to be able to add extra advice in the auto generated product purchase emails, like store policies, general product information etc...

They look like text only. Thought they were HTML before. “Use MIME HTML When Sending Emails” is set to true. They appear like text emails though.

V 1.3.9h

Ahh I can see the HTML or TEXT emails is set by the store account user, via an option they have when they log in.

On another note. Is there a way to force HTML only emails ? Would prefer that or at least have them default to HTML initially with the customer option to turn off. I think the HTML looks better than text and is easier to read. Nowadays near everyone is happy to accept HTML emails. Especially we now have broadband internet.

Text-only emails are built from text defines located in your language files, whichever language file is used for each page. So a create-account email will use the create-account language file when finding content for email messages. Plus the email_extras language file.

HTML-formatted messages are built from the SAME defines in the language files, and then the content is assembled based on the instructions in the email templates in the /email/ folder. So to make changes to BOTH formats, you would do your changes in the language files directly, since those will be reflected in the HTML version as well. If you're making additions, then you really ought to just add them onto the existing language defines, and NOT create new ones, else you'll need to make many programming changes to incorporate new ones in all the places they belong.

You can change the email "default" preference from text to html in Admin->Configuration->Customer Details. This will affect only future customers, not existing ones.

Ahh ok thanks. I was going to edit the html email template, but wasn't sure if there was another recommended approach. I guess that is the approach.