The algorithm used by Gmail to decide which tab emails are delivered to is very complex and is based on many factors: the content of the email, the sender reputation, the sending infrastructure, and user behavior/interactions (the more users open and click on your emails, the higher the chances that future emails will be delivered to the Primary tab).
Completely avoiding Gmail’s Promotions tab is difficult because it doesn't depend solely on technical settings.
Usually, it is recommended to try to:
- personalize the email as much as possible
- minimize the presence of images and links in the content
- remove any overly promotional or commercial wording
However, even by following these best practices, there is no guarantee that your emails will actually be delivered to Gmail’s Primary tab.
Delivery to the Promotions tab should not be seen as negative or compared to spam, because it is still a form of inbox delivery.
Moreover, studies and analyses conducted in the past have shown that the introduction of the Promotions tab did not result in any performance drops, not even in open rates, because Gmail users are familiar with the tab and check it regularly.