There's something of a hoo-haa blowing up after it was revealed that Yahoo was testing technology to prevent users with adblockers enabled from reaching their email service.
Aside from the way it was done - surely a warning was in order before implementing such a drastic response - I don't have any issues with Yahoo's actions here.
The email service is provided free and I'm sure that the T&Cs include the warning that receiving ads is a fundamental part of the service.
No doubt Google and Microsoft, as well as other ad-funded mail services will be investigating the same responses right now.
For those criticising Yahoo's actions here a reality check is in order. There is no such thing as a free lunch. Ads are the price you pay for the email service that Yahoo provides you. Block the ads and Yahoo is entitled to block your access to the service, just as any other utility would cut you off for not paying your bills.
So suck it up. Either switch to a paid email service where you don't receive ads or turn off your adblockers and suffer the ads in return for an otherwise free service.