How can I check if an e-mail was opened?

Question

I'm looking for a reliable way to check if user opened an e-mail which I sent to him. I know I can use some images generated by PHP script (and save client headers / data on server-side), but my question is - is this reliable? Some web clients have disabled images by default, I'm not sure about proxy severs, BlackBerry etc...

So - Is there a good and reliable solutions to this problem?

Thanks.

Answer 1

There is no reliable solution (and I'm glad there isn't). If the user only views your mail as text then nothing (besides the mail itself) gets downloaded or anything like that.

Answer 2

The one and only solution unfortunately doesn't exisist. Some email service providers use a tracking pixel, some use an external css file, some track images + clicks, some track the request of any image within the email, some even try to incorporate nifty tags like bgsound. And some do it all combined.

The only ones who can report real open rates are those who have direct access to the users inboxes: the internet service providers themselves and software providers who develop apps and plug-ins for gmail, outlook, & co. Some of them report real open rates to marketers. Like Mail.ru, OtherInbox, and eDataSource. But for obvious reasons, this all isn't perfect either.