If you've noticed Gmail placing your messages in the Promotions tab, there's no need to worry. The Promotions tab is still the inbox.
What is the Promotions Tab?
The Promotions tab was created to keep any kind of promotional or marketing message in its own folder. Messages that land here will not cause any sort of push notification for the Subscriber, and it will not contribute to their unread message count.
While this might mean Subscribers don't see your message as quickly, it also means they're less likely to unsubscribe or mark your message as spam due to unwanted notifications or a flooded inbox.
What belongs in the Primary tab?
Gmail intends for the Primary tab to contain important 1:1 messages that are more transactional in nature. However, we have seen that if a Subscriber is highly engaged with a sender, it's likely that even the sender's promotional emails will land in the Primary tab for that specific Subscriber.
How does Gmail determine if a message belongs in Primary or Promotions?
Gmail uses advanced algorithms to determine whether a message should land in the Primary, Social, Promotions, or Updates tab, and they don't give out information about how this decision is made.
We do know it's generally based on the overall content of the email, and the sending relationship between you and your subscribers.
Why the Promotion tab can be a good thing
It helps keep marketing messages out of the spam folder.
Your messages are more trusted and more seen since they are kept out of the spam folder.
Subscribers are less likely to mark the message as spam or unsubscribe since these messages aren't causing notifications or filling up the primary inbox.
Want your messages to land in the "Primary tab"?
Trying to outsmart Gmail's filters to achieve Primary placement isn't a productive strategy. Instead, you can encourage your subscribers to drag your message from the Promotions tab to the Primary tab so that Gmail's filters are trained to always place your emails in the Primary tab in the future.