Add List-Unsubscribe Header To Newsletters

Hi, CS-Cart Team,

what about adding additional custom header, defined in RFC 2369

List-Unsubscribe: , <%UNSUBSCRIBE_LINK>

to the default email headers generated by PHPMailer while sending newsletters from CS-Cart?

All major cloud email providers, including Gmail, respect this and provide a better UX for clients who are looking for unsubscribe button.

Additionally, in Gmail it would help newsletter to be correctly classified as "Promotion" and to reach the respective tab. Please check:

All major email-marketing services, incl. Mailchimp, SendGrid, etc. have it, but CS-Cart built-in newsletter engine lacks it, and that is why our emails score more spam-points.