Hi,
Where the emails end up in your GMail account is not something that can be controlled by WunderAutomation (or any other emailing tool for WordPress).
Google makes this classification on a case by case basis for each email by analyzing multiple factors like number of links, the language you use in the email body, your domains reputation etc. This is pretty much the same situation as with spam handling, it’s the receiver email client/system (Gmail in this case) that determines what it thinks is spam or promotional emails. You’re going to need to fine tune the content of the emails you send out.
Cheers,