Is Gmail’s new tabbed inbox reducing the effectiveness of email newsletters?

This article has been updated to reflect Google’s comment.
While Gmail’s new tabbed inbox system has been around since May, Google has been rolling out the program  to users in stages this month. And as people get used to the new inbox, which sorts their mail by type, there may already be a casualty of the system.
Matthew Grove of email and newsletter distribution platform MailChimp wrote a blog post suggesting that the new Gmail may be reducing the effectiveness of its email newsletters. It came to that conclusion after looking at the “open rate” of billions of its emails sent to Gmail. In the new Gmail, newsletters are filtered out of the “Primary” tab — where essential emails are sent — and put in the “Promotional” tab, along with spam, flash deal offers and even Google’s own ads. As a result, their contents may be more apt to languish in the inbox unseen.
Grove writes:

What bothers me in this case is that open rates stayed down for 3 consecutive weeks. From looking at a year and half’s worth of data, I can say that kind of behavior isn’t normal. I’m not willing to declare an emergency just yet. After all, I don’t even know what the adoption rate is on Gmail’s side. However, I would say this is an early indicator, and we’re definitely keeping our eye on it.

Grove says that while the company has tinkered with the content and style of the emails to try to get them to land in the Primary stream, it hasn’t been able to crack that code. It’s likely that no matter what MailChimp and other newsletter developers devise to get out of Promotions, Google and its Gmail team will be there to counteract the techniques. After all, users have opted in to have the Promotions tab — if they wanted to see promotions in their primary feed, they would configure accordingly.
When asked for comment, Google reiterated the user’s choice in to include the promotions tab, or avoid it entirely:
“If you prefer another inbox style, you can choose from any of the four inbox options or even customize the new inbox by dragging and dropping messages to different tabs or electing to have certain senders always get sorted into a particular tab.”
It’s, of course, too early to reach any deeper conclusions about the lasting impact on email marketers from the new Gmail inbox– and we have reached out to other email providers to see if they’ve had similar experiences, as well as to Google to get their reaction. But if this pattern holds, it could be problematic for companies that rely on newsletter communications to survive and thrive online.