Enhance email headers and body

The email headers for the price alerts aren't complete and may lead to the emails being bounced back as spam. The body of emails was put together very quickly and may also result in emails being bounced back as spam also, as small plain text emails are regrettably thought to be spam by many email providers. Dressing up emails with some simple HTML content would increase the likelihood of email delivery, which is a must-have for this project.

Locate the code that constructs and sends price-alert emails, then inspect how headers and the plain-text body are currently assembled. Determine the required delivery-safe headers and the intended simple HTML presentation before making changes; done means price-alert emails include complete headers and an HTML body that improves delivery reliability.

Written by the indexing model from the issue text.