I'm owner of a day-spa and I've read on several places that a reservation email (like hotel booking) send to Gmail can show up automatic in Google Calendar.
Do you need to do something special with these reservation emails? Like to put in a code or something?
The markup you're looking for is schema data that needs to be embedded in the email HTML.
You can find details of it in Gmail's reference docs: https://developers.google.com/gmail/markup/reference/hotel-reservation
Gmail will then scan the e-mail and in most cases automatically generate the associated features for a user.
