How does Litmus track their email analytics?

Question

So, \'Litmus\', a web app for testing emails and webpages across browsers and email clients, has a proprietary method that they claim is able to track not just opens, clicks

Answer 1

It's all done with good ol' image bugs. Breaking down how they find out...

• Which client was used: Check the user-agent

• Whether an email was forwarded: Done by attaching image bugs to divs that are loaded only when the message is forwarded.

• Whether an email was printed: bug attached to print stylesheet

• How long it takes to read an email: A connection that's kept open, as pointed out by Forrest (this is also how Facebook tracks(ed?) whether or not you are online on chat).

• Whether an email was deleted: Check If a message was read for a short period of time or not opened. In fact, they group "glanced" and "deleted" together.

Of course none of this will work if email clients disable images in emails.

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EDIT: Here's another question on this:

The OP actually has their tracking code, and this answer here explains how it works.