We currently have multiple emails (marketing and newsletter) that we send daily to millions of users, sent from separate sender emails (same domain, not using email subdomains).
We're currently unclear when or how emails go to a user's "Promotions Tab" vs. regular Inbox. We definitely prefer that our emails show up in the user's Inbox and NOT the Promotions Tab, because we don't want our emails (whether marketing or newsletter) to get buried in a user's inbox.
If we use the Gmail Promotions Tab Annotations, will that ensure that our emails definitely show up in the Promotions Tab, or will our special annotations (i.e. banner image, promotion code, expiration) ONLY show up if it so happens that our email is in the Promotions Tab?
No, according to Google's FAQ, adding the annotation will not force the email into the Promotions tab. See here: https://developers.google.com/gmail/promotab/faq