In another life, when I'm not ranting and raving about this or that, I work in Internet retail. The company I work for sells stuff through a secure website with a shopping cart and ships product to customers around the world. Now let's bring Gmail into the conversation.
As part of the sales/shipping cycle we communicate with our customers via email. First, at the point of sale we send the customer an order confirmation email listing the products they ordered, the amount they paid and the shipping address they provided - no links, no ads, nothing but the basics of the customer's order for their records and review. We also then send the customer their tracking number at the time their order ships - again with no ads or other BS.
Along with direct replies to customer service inquiries that's the sum total of the emails we send, but Gmail has decided to spam them. The company has jumped through all of Gmail's hoops, sent several inquiries and gained no traction whatsoever.
The end result has been a glut of angry calls and emails complaining: "You've taken the money off my card, but I never got a confirmation or anything - what's the deal?"
Okay, all fine and dandy, I have a valid complaint, but I've asserted that Gmail doesn't get it. I can back that up with basic logic.
Gmail has aggressive spam filters so that Gmail users don't have to scroll through page after page of spam - a good goal by any account. Unfortunately, the filters have gone one tick too far and now online merchants are stuck telling Gmail users "please check your spam folder, scroll through page after page of spam and mark the order confirmation email as not spam, or you'll never get the tracking number either."
Gmail's filters, designed to protect users from seeing all that spam, are now so aggressive that false positives are forcing users to review their spam folders. Rather than seeing a couple unfiltered spam emails in their inboxes, Gmail users are now forced to scroll through hundreds of spam emails to find a needle in a haystack...