There is no official “primary inbox” switch. Gmail’s classifiers look at bulk headers, similar copies to many people, image-to-text ratio, unsubscribe language, and how users historically treat mail from your domain.
What pushes you into Promotions
- Single large hero images and sparse text.
- Discount language, countdown urgency, and multiple tracking links.
- List-Unsubscribe plus campaign-style HTML sent to thousands at once.
- A From name that is a brand, not a person, especially on mixed-use domains.
What actually helps
Send mail people reply to. Conversational text, a real signature, and a domain they already trust for one-to-one mail all help. Do not pretend a newsletter is a personal note if the body is still a three-column promo. Users train Gmail when they drag you to Promotions; they also train it when they reply.
Split transactional and marketing
Receipts, password resets, and shipping mail should come from a dedicated subdomain with a different template. Mixing abandoned-cart blasts onto the same domain as password resets teaches Gmail that everything from you is marketing. Keep authentication aligned on each subdomain.
