A: Gmail is sorting these by content, not by authentication. SPF, DKIM, DMARC, and your own SMTP already did their job: the messages are delivered. The Promotions tab is a separate filter, and a review request with a logo, a button, and a tracking link looks like marketing mail to it. Nothing in the setup can force the Primary tab. Rewrite the subject and body as a short note from a person, such as "Thanks for coming in yesterday," set the sender name to a staff member with reply-to on a real inbox, and in Email settings set List-Unsubscribe headers to Exclude. Test from a new Gmail address that has never received one, because the inbox you have been testing has already learned this pattern, and moving a message to Primary only trains that one mailbox. If you have a custom link domain, use it so the review link is on your domain. Even then, Gmail may still choose Promotions. That tab is still the inbox, and we cannot guarantee Primary for this kind of email. Text messages skip Gmail's tabs entirely.