If your mail appears to be promotional in nature, then it belongs in the Promotions tab, and that is where Gmail will present it unless a preponderance of your recipients are engaging with it in such a way as to indicate it belongs in a different tab.
Generally speaking, important and one-to-one correspondence will be presented in the Primary tab, social media in the Social tab, news alerts, newsletters, transactional mail will display in the Updates tab, and list traffic in the Forums tab.
Mail displaying in any of these tabs are, by definition, in the Gmail inbox.
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