Is there any way to track whether an email has been opened?

I have been looking for an answer to this question for a few weeks now and found several options out there. The one I like will send the 'open' data to Google Analytics.

The image below should be inserted into the body of your email. Each person I send an email to has a unique customer number so i can see opens/unique opens but it must not identify a specific customer according to Google's terms.

            <img src="http://www.google-analytics.com/collect?v=1
                &tid=UA-12345678-1
                &cid=12345
                &t=event
                &ec=email
                &ea=open
                &el=recipient_id
                &cs=newsletter
                &cm=email
                &cn=Campaign_Name
                " />

Mail clients block pretty much all of these kinds of attempts. The best idea is to give them an image that they would want to see if they read the message, and therefore they choose to display images in their mail client.

There is no bulletproof way to check if a user has read your mail. And there shouldn't be IMO.

You can ask for a read receipt (an email feature), but most users consider this a real pain.