As a result of recent changes in Google’s popular Gmail product, newsletter publishers need to take a close look at slimming down their subscriber lists to prevent readership from plummeting.

Email services have long tended to punish newsletters that are sent to large numbers of “spam traps” – AKA abandoned email addresses – sometimes shunting them to spam folders or blocking them altogether. So the need to weed out subscribers who never open a newsletter is nothing new.

But Google upped the ante late last year with Gmail, which serves more than half the subscribers for many consumer newsletters. (The changes were presumably rolled out as well to G Suite, the Google product that underlies many corporate email systems.)

“Gmail began to penalize senders more heavily for longer-term inactives—those subscribers who hadn’t opened or clicked in more than 180 days—and there was some intermittent spam folder placement and a reputation drop as a result,” says Clea Moore of Oracle CX Marketing Consulting. That led to a noticeable drop in open rates for email campaigns that Oracle’s clients sent to Gmail addresses.

There are two takeaways for publishers: