From MozillaZine Knowledge Base

This article was written for Thunderbird but also applies to Mozilla Suite / SeaMonkey (though some menu sequences may differ).

Return Receipts

One way to tell if a person has read your message is to request a return receipt. If you select Options -> Return Receipt when composing a message it will add a header to the message that requests the recipients email client to send a reply. It does this by adding a Disposition-Notification-To: header that specifies who to send the reply to. However, you can't rely upon this because many email clients let the user decide whether to ignore return receipts, or to decide on a case by case basis whether to allow the return receipt.

"Tools -> Account Settings -> Return Receipts" lets you specify what Thunderbird should do when it gets a request to send a return receipt, for each account.

Email tracking

A unscrupulous way to tell if somebody read your message is to send a HTML message that retreives web bugs from a remote server. A web bug is a graphics image too tiny for a user to notice it. If the server logs the request then you have proof the recipient read the message. Unlike return receipts, this can be done secretly. Usually you have to use a proxy (and have the service send you the return receipt) or use the service's web page to send the message and check on its status. This is the reason many email clients provide an option to disable loading remote images.

Some of these email services make more sophisticated use of HTML. For example, ReturnReceipt uses IFRAMEs, bypassing most email clients attempts to block loading remote images. Currently only a few email clients such as Kmail are able to disable that call, while still displaying the message as HTML.

Some ways to defeat email tracking:

• Reading the message while not connected to the Internet is the safest and most reliable way.
• Viewing the message as plain text using "View-> Message Body as -> Plain Text" is a good solution, as long as you don't click on a link or open an attachment.
• Disabling loading of remote images using Tools -> Options -> General is very convenient, but its useless against some of the more sophisticated services.
• Make a connection through a proxy such as Proxomitron that is configured to run filters to remove web bugs and disable IFRAMEs.

If you're trying to figure out whether a recipient read your message there doesn't appear to be any way to quarantee it as long as you're using different mail servers. The recipient can disable a request for a return receipt. All of the tools and services for email tracking appear to rely upon the recipient either not being technically knowledgeable enough to protect their privacy, that its too much of a hassle for them to take the necessary precautions, or that they don't care.

See also

• Recall a message

External links

• Some well known email tracking services/tools
• Email privacy is lost article at Security Focus
• Proxomitron resources
• Message Disposition Notification RFC
• MsgTag