In the last few years, phone tapping and email interception has become rampant.
This article on email interception and phone tapping in India explains how it is done.
It appears that many times this facility is misused to harass people or get information on business rivals. A month ago , emails sent to 2 of my email addresses disappeared. I contacted the ISP , who gave me complaint numbers , but are unable to give a logical explanation for the same even after a month.
I hope there will be greater transparency in the system in future.