Just as retail stores are sending their final marketing emails, trying to eek out any last minute sales this holiday online shopping season, experts are out with new data showing how retailers fared after a Gmail interface shakeup this year.

Six months ago, Google began rolling out a new feature in Gmail, which automatically sent marketing emails away from users’ primary inboxes and into a seperate tab.

Recently, analyses from several organizations seem to confirm what most marketing teams have always believed to be true -- this tab is bad news for mass emails. 

The numbers generally show that open rates of retail emails in Gmail have declined compared the open rates during this time last year, according to The New York Times’ Bits blog. From the article, here is what three different marketing email services found:  

Gmail’s edge over Yahoo is dwindling. Email marketers used to hope that their messages landed in Gmail inboxes. Gmail users clicked on retail emails 14.5 percent more than Yahoo users before the introduction of the "Promotions" tab, according to Epsilon. Now that difference has decreased to 4.2 percent.

Retail emails saw less opens on Cyber Monday. Open rates of marketing emails in Gmail inboxes declined 7.5 percent on Cyber Monday. However on the same day, open rates collectively increased 15.7 percent at Yahoo, Hotmail and AOL, according to Sailthru.

Over six months, opens and clicks are down. MailChimp found that over the past six months, open rates at Gmail declined 1.6 percent, and click rates declined 1.4 percent.

However, there is a silver lining. Sailthru found that Gmail users who opened a retail email were more likely to spend money compared to those using any other email service. The finding seems to underscore what those who favor the change believe: if shoppers really intend to make a purchase, they’ll seek it out. 

“If those subscribers asked to hear from you and most likely signed up for your list because they wanted to receive special offers, deals and discounts from you, then why is everyone worried about having their e-mail delivered to a tab that was created for that very purpose?” Inc. contributor Janine Popick has written

“Now instead of being mixed in with e-mails from your mom, or updates about your latest wine shipment, your offers and deals get placed in one easy tab for viewing.”