I've written an email application in PHP that handles very large mailing lists. Is there a way to find out what emails are opened and by who? Any solution will do as long as it can tell me if the user has actually received and opened the email. I do not want to use email receipts either as it may put off recipients.
If it's relevant, I'm using the codeIgniter framework.
You can put a tiny invisible img in each email, each image named differently to corespond with a specific email. Then you parse your access logs and see which images have been requested and you know which emails have been opened.
It's not fool proof but i've seen some companies use this method.
You can accomplish this by including a small tracking image in every email that is sent out.
<img src="http://yourdomain.com/tracking/1x1.gif?cId=12345&uId=56789">
Use mod-rewrite to push everything beyond '/tracking/' into your analytics script, snag the query_string and return a 1x1 gif to the email clients.
From Campaign Monitor:
http://help.campaignmonitor.com/topic.aspx?t=89
When each email is sent out, we automatically add a piece of code that requests a tiny, invisible image from our web servers. So when a reader opens the email, the image is downloaded, and we can record that download as an open for that specific email.
It is important to understand that the open rate is not a 100% accurate measure. Recording an 'open' can only happen if the reader's email client is capable of displaying html with images, and that option is turned on. So if you are sending text-only emails, there is no way to record open rates. Similarly, people reading your html email without images showing will not be recorded as opens (unless they click a link).
Another issue is that your readers may have a preview pane in their email client. That preview pane might be displaying your email automatically (and therefore downloading the images) without the reader ever having to click on it or read it.
So you should never take your open rate as a hard and fast number, because you can never know the true figure. It is much better used as general guide, and as a way of measuring the trends on your email campaigns.
There's read receipts, but those are only supported by specific clients (ie, Outlook), and even then they are given the option to not notify you of their reading it.
The only other option is to communicate with your server when they read the email. To do this, you can implement a tracking pixel, which is a 1x1 transparent gif. You can intercept the response on your server and log the time, date, ip address, etc.
This still isn't foolproof though, because some clients such as gmail don't show images by default.
You can read more here: http://en.wikipedia.org/wiki/E-mail_tracking