Last week, Google added a new feature in Google Apps that allowed educational institutes and organizations to track how people are interacting with Gmail messages.
Anyone with admin access in Google Apps can see basic visitor stats for Gmail messages including length of visits, geographic location, what browser are they using to read their emails and so on.
This email tracking feature via Google Analytics is now available across all Gmail accounts though you will have to enable it manually via GMail labs.
Once Google Analytics is enabled, go to the General tab in Gmail Settings and type your Google Analytics Tracking code which is of the format UA-xxxxxxx-y where ‘-y’ refers to the profile number. Always create a separate Analytics profile for tracking Gmail messages else this can inflate your existing site impressions.
Though Google Analytics for Gmail will only provide very basic information about email recipients and there’s no support for read receipts, this could still be seen as a privacy risk by some because there’s no way for you to prevent Google Analytics from tracking your interaction with a Gmail message unless you block the Analytics script itself on the computer.
I will also be more happy if this is an "opt in" feature for the recipient so that he or she can decide whether the email sender should have access to their information or not – this is how you have in Microsoft Outlook.
Related: Track Email Clicks with Google Analytics