My emails are going in the Promotions tab, how to prevent this?

The "Promotions" tab is a Gmail-specific feature. As Google states:

"Gmail automatically groups and highlights emails in the Promotions tab that people are most likely to engage with."

Further clarifying:

"These are not ads and happen automatically based on a number of factors."

Google launched its Gmail tabs feature in 2013. Today there are solid statistics available about the behavior and adoption of users that debunk some of the myths and misconceptions about the Promotions tab:

Emails in the Promotion tab have a read rate of 19.2%. (Source)
The Gmail primary tab has a read rate of 22%. This means promotional emails are read only 12% less than the personal 1-1 emails in the primary tab.
1 in 5 Gmail users has the Promotions tab enabled. This number is constantly decreasing as the number of people disabling the Promotions tab is far larger than the number of people who enable it. Most people disable the tabs feature once they start using Gmail.
45% of the people that have this feature enabled check the Promotions tab every day.
Only 20-30% of the email addresses on a typical email list are Gmail users, and 1 in 5 people has the tabs enabled. That means that only about 5 to 7.5% of your audience has the Promotions tab enabled.

Considering the small difference between the open rates in the primary tab and the Promotions tab, it's safe to conclude that the negative effect on your open rate due to landing in the Promotions tab is going to be negligible – less than 0.5%.

In other words, while it's often assumed that people prefer to read personal emails, the fact is that they treat the Promotions tab as an extension of their inbox, and the engagement rate is just slightly smaller than the primary tab. The misconception that the Promotions tab is just another spam folders, is simply not true.

How the Promotions tab works

Gmail uses an extremely advanced algorithm that sorts emails based on various factors that are impossible to track. This smart algorithm monitors closely what emails each person is most likely to engage with and sorts email communication based on the personal behavior and preferences of each user. In fact, this sorting algorithm is so good that 9 out of 10 Gmail users say it sorts their emails correctly.

There are thousands of factors involved, and no "silver bullet" that will cause your emails to get sorted a certain way. It's simply not possible for an email marketer or an email marketing service to "outsmart" the algorithm, and don't listen to anyway who tells you otherwise.

Bottom line

The impact of the Promotions tab on your email engagement is so tiny that it's not worth fighting for it. Even if you want to "force" emails to get in the primary tab, there is no way to trick Gmail into sorting your emails one way or the other.

Still want to land in the primary tab rather than Promotions tab?

While it's not possible to force Gmail to put your emails in the primary tab, there are some best practices that you can apply:

Remove any images in your emails.
Remove excessive text formatting.
Keep links to a minimum.
Use the Simple email editor instead of the Drag and drop email editor.
Avoid any HTML styling and use plain text only.
Personalize your email with merge tags and liquid tags as much as possible.
Make the From and Reply address match.
Disable reply tracking if you have it turned on. (Note that it's turned off by default).
Add your email domain.
Remove any promotional words in the subject line and body copy. E.g., "Free", "Act now", "Buy", "Offer", "Discount".
Keep the email relatively short but no shorter than a couple of sentences, otherwise, it might look like a test email or spam.
Declutter your footer – remove any social links, images, etc.

Note that there's no guarantee that these recommendations will work. Alternatively, you can simply advise your audience to disable the Promotions tab for their Gmail account. You can provide them with the instructions here.