Gmail created the Social and Promotions tabs in Gmail to allow users to keep their primary inbox free of clutter. Google scans the incoming email and, depending on the content, may funnel it into the Social or Promotions tab as seen here:
Two important things to remember about the promotions tab:
This view allows a user to view a segmented inbox. Landing in the promotions folder is not like landing in the spam folder; the email is simply routed to a different section of the receiver’s inbox.
Any time you send out bulk email, especially anything that contains special offers, time-sensitive deals, or straightforward promotional content (sweepstakes, giveaways, etc.), those messages are more likely to land in the promotions folder – that is specifically what it was designed for. Ultimately, Gmail and the end-user are in control of what lands here.
As Gmail relies on user feedback, first of all, you need to segment your list and ask your Gmail subscribers to drag your email from the Promotions to the Primary tab in their Inbox. Folderly helps you get rid of that kind of headache and help you get right into your subscribers' inbox.
From our best practices, make sure that your email does not look like promotion and keep in mind the following things:
Remove images or try to reduce them as much as you can;
Reduce the number of links to 3 or less;
Change the standard footer added to the email by your Email Service Provider (ESP). Mailbox providers like Gmail and Outlook use your unsubscribe footer message to detect a promotional email by analyzing email body content.
For example, you can change the "Unsubscribe from this mailing list" text to "Unsubscribe" and remove the "View in Browser" link;
Change the tone of your message. Marketing emails can feel redundant after a while. Test what kind of tone resonates with your contacts the best. Maybe your messages can be more playful instead of professional.
Encourage subscribers a reply to your emails. This is one of the general metrics for Google before deciding where to place your message.
Read more tips on how to get your email delivered to Gmail's Primary inbox here.