Is there some kind of official announcement from Yahoo & Gmail if they monitor emails of people like claimed by wikileaks or they have stopped monitoring the emails now? I have little knowledge about this and thinks this matter has not been discussed here before.
There's no official announcement but basically Google has been saying: we've tried to resist but it's the government. We know that Gmail's business model is based around reading your emails to determine your interests and purchase habits for targeted advertising. If by monitoring you mean the government then yes, their servers intercept the data as well. Yahoo was recently sold to Verizon and right after the deal was made, it became very public that they originally offered everyone's data straight up. Verizon then wanted their money back
Mails are being monitored but only for special reasons. To detect shady deals and fraudulent acts. However, I think the user's privacy is still strictly followed as you are not prone to being hacked.
If anyone thinks that any emails that they send or social media posts they publish (privately or not) are not monitored by a wide range of government agencies around the world, that person is in for a rude shock. There is zero privacy on the Internet. Period.