According with a post in the Adblock Plus user forum, Yahoo appears to block access to company email users if they use adblocker.
Several users mentioned exactly the same thing and while they were trying to see their inbox, they found themselves in front of a message saying:
Oops… We are unable to show you Yahoo Mail. Please turn off Ad Blocker to continue using Yahoo mail.
In a statement to the Bits Blog of the New York Times, MsfaceCompany CEO Anne Yeh said:
“At Yahoo, we're constantly developing and testing new things products. This is a trial run for a small number of users Yahoo Mail in the USA "
Advertisements are the main source of revenue for publishers providing free content online, and the popularity of new mobile ad blockers seems to worry Companies as loss of revenue is certain.
Yahoo seems to be the first major company to try to block basic services for users who choose to use an ad-blocker, proving in practice that they are more interested in advertising than their service users.