• by Jess Nelson , November 20, 2015

Yahoo Mail has begun restricting email access for ad-blocking users this week, an act likely inspired to safeguard falling advertising revenue from the free email service. 

Reports suggest that an error message from Yahoo reads: “Uh oh… We are unable to display Yahoo Mail. Please disable Ad Blocker to continue using Yahoo Mail.”

The company is reportedly testing a lockout system for users who have installed ad-blocking software on their devices. “This is a test we’re running for a small number of Yahoo Mail users in the U.S.,” confirmed a Yahoo representative to Business Insider and Engadget.

Yahoo’s move is not surprising, given the growth of ad-blocking software in the United States and the company’s falling revenues. Yahoo’s net income for third-quarter 2015 was only $76 million, a stark contrast from the gain of $6.77 billion in third-quarter 2014.

Ad blocking has cost publishers an estimated $22 billion in advertising revenue within the first six months of 2015 alone, according to an August study by PageFair and Adobe.

Some 9% of U.S. Internet users now block ads, via comScore and Sourcepoint. This number is significantly higher in Europe, where a quarter of French (27%) and German (24%) Internet users block advertisements with ad-blocking software.

Although 9% of the U.S. population may seem peripheral, the number is rapidly growing. By June 2015, there were an estimated 198 million active ad-blocking users around the world. Ad blocking in the United States grew by 48% year-over-year in 2015 to reach 45 million active users, while ad-blocking users grew 41% globally, per PageFair and Adobe.

The monetization model of free email providers such as Yahoo Mail and Gmail has been largely focused on advertising thus far, but increased ad blocking means that either email providers will need to pivot on their monetization strategy or marketers will need to innovate advertising with more relevant, personalized opted-in content that will not raise the ire of ad blockers.