It’s been the talk of the email town in the retail space these last few weeks: Gmail’s new email filter.

Nobody seems to love it, especially retailers.

If you aren’t a Gmail user, or didn’t know, here’s the scoop. The new email system separates users’ emails into three distinct tabs: one for “Primary,” one for “Social,” and one for “Promotions.” Naturally, the majority of retailers’ email are going to go straight into that Promotions tab. This means that even those promo emails customers might actually want to see could easily be missed. In fact, there have been reports of retailers emailing their customers saying things like, “We haven’t forgotten about you,” and, “We’re still here,” because they know customers are missing their messaging when they may not want to be missing it.

To make it even trickier, for the Gmail users that do happen to visit that Promotions tab, the first items they see will often be ads from Google that look like emails sitting in an inbox but are shaded yellow and feature informational “i” icons explaining their purpose. Marketers are complaining that the ads threaten to draw attention away from the coupons and pitch emails they want their targets to read first.

“People are not very amused by those,” said Tom Monaghan, product manager for the email service at marketing service HubSpot Inc., to Wall Street Journal writer, Drew Fitzgerald.

The one saving grace is mobile: Gmail users can’t see the changes when accessing their messages on iPhones. Ms. Freund said more than half of all users have the updated Gmail layout, which the company has been gradually rolling out since May.

Big emailers like Delta Air Lines Inc., Gap Inc., Gilt Groupe Inc. and Groupon Inc., have sent step-by-step instructions to their mailing lists on how to move messages out of the Promotions tab and back to Gmail’s “Primary” folder.

Marketers fear the new system could spread and put an unwanted kink in a tried-and-true method of driving sales, not to mention business models that rely on emailed coupons.

“Let’s stay together,” apparel retailer Kate Spade Saturday pleaded in an email to its newsletter subscribers. Gmail’s “new inbox settings may have started filing away your Saturday.com emails into the depths of something called a ‘Promotions’ tab.”

“Ack,” it added.

Analysis from HubSpot showed the percentage of Gmail users who opened clients’ emails slid slightly over the summer, though activity spiked during the weekends. Open rates have declined at the same slow rate since April, suggesting user engagement is suffering from too many emails rather than Gmail.

Gilt, an online service that alerts members to deals on luxury goods, said it hasn’t had any problems with Gmail’s new layout. “Having said that, we think the best thing to do is to educate our members,” said Elizabeth Francis, the company’s chief marketing officer.