Why do newsletters arrive at Gmail under the Promotions tab?

Since autumn 2013, Gmail emails have been coming in under different tabs. One of them is the Promotions tab. 

Almost all newsletters automatically arrive at Gmail under this tab. Your subscribers may see this tab as a folder for unwanted advertising, which it is not. The exact reasons for Gmail sorting emails into a particular tab are unclear.

To prevent your Gmail subscribers overlooking your email, you can ask your them to make a small change in Gmail if they appreciate your newsletter. You can present your Gmail subscribers with three options:

• First, you can ask your Gmail subscribers to move your newsletter from the Promotions tab to the Primary tab (the personal inbox). Gmail then asks if all new emails with the same sender address should also be placed under the Primary tab. The preferred answer is, of course, yes.
• Secondly, you can ask your Gmail subscribers to mark interesting newsletters with a star. Starred newsletters are listed by Gmail not only under the Promotions tab, but also under the Primary tab.
• Third, you can ask your Gmail subscribers to switch off the Promotions tab completely. All emails that automatically arrived under the Promotions tab will then be received under the Primary tab.

It goes without saying that the first option is the best for you.