Gift certificate emails not using template

This is ZC 1.5.0, with CSS/JS loader and Fast and Easy AJAX checkout installed. I have modified the Picaflor Azul Avonlee Contempo template for the client's branding. I have searched for similar issues and checked my settings, but I'm still getting text only gv emails.

I have gift vouchers installed, and they work correctly. I have no error messages. But when I send, as a customer, a gift voucher to someone else, the emails arrive as only text, even though I can see templates in the email directory, and I have modified them (email_template_gv_mail, *_gv_queue, *_gv_send). I know in 1.3.9 (a different cart installation) I got at least a logo at the top of the email, and that is defined in the template of this cart, but the gv email function doesn't seem to be picking the template up at all.

I have email options > use MIME HTML set to true, I have customer details >default email preference set to HTML. The site is at http://www.44steaks.com/_bigtest/. The client wants to use an HTML email with an image of a branded gift card, and I'm befuddled as to why the template isn't getting picked up. I have tried sending emails to other existing customers in the cart, and to addresses which don't already exist. All arrive as only text instead of using the html template.

Any clues will be greatly appreciated!

If the recipient doesn't exist as a customer in your store, they will get a text-only version of the message, because they haven't had a chance to opt-in to HTML-formatted emails.

Thank you DrByte. The client won't be happy, since they have corporate customers who want to send pretty, branded, html gift certificates to employees whose email addresses won't already be in the system, but I understand the logic here.

I created a customer account, customer1, and purchased a gift certificate. I created a second customer account, customer2, and selected html as my email preference. I logged in to customer1 and sent a gift certificate to customer2. The certificate arrived as only text. Is there something I'm missing?

Install the Email Archive Manager plugin, and turn on email archiving. Then do your test again. See whether it shows the HTML portion as blank or not.

If the HTML portion is not blank, then Zen Cart prepared and sent it, but your email client isn't reading or receiving it.
It might have been stripped by spam trappers ... which is unsurprising if you haven't taken good care in building the email content. Sending HTML emails takes some careful forethought if you want to avoid spam traps. You can see some best-practices info on the Mailchimp website's FAQ articles.
Spam trapping is also more aggressive when you use the "PHP" setting for Email Transport instead of "SMTPAUTH" in your email settings.

If the HTML portion in the archive is blank, then Zen Cart didn't prepare an HTML section for the message, because customer preferences weren't set to HTML.

I knew our other HTML emails were getting through fine, and the HTML portion of the gift voucher message was not blank in the Email Archive Manager HTML area, so I decided to look back through the customer list. There was a previous test customer in the database with the same email address as the one I was using, with email preferences set to text. Once I deleted that, the HTML started showing up.

Thanks for your help, much of this exercise has answered other questions the client had.