A service that automatically notifies the sender that an email message was previewed or opened by the user. When users send mail from their email clients, they can ask the recipient for a response, but that person has to oblige that request. On the other hand, email trackers do not rely on the recipient's cooperation and automatically send a response. Some services silently return the receipt, while others place a note at the bottom of the message indicating a receipt was sent.
The read receipt indicates the time the message was previewed or opened, as well as possibly the location of the recipient's computer and the duration the message was kept open. See read receipt
A Web Bug Does the Trick
The tracker software in the user's machine inserts a Web bug into the message, which is an invisible GIF with a unique name obtained from the tracker's server. When the recipient previews or opens the message, the GIF is downloaded from the tracker's server, which reads the name and notifies the sender. If mail was relayed to a text-only, handheld device, the Web bug will not work because the email must be displayed via HTML and be online to the Internet. See Web bug
Two Tracking Methods
The first method requires a software installation in the user's machine; either a plug-in for Outlook or a program that resides in the background for other email clients. When messages are sent, only the unique GIF names are downloaded from the tracker's servers. However, this method generally does not work when a Web browser is the email client.
The second way is to route the message through the tracker's server by adding a suffix to the address. This method works with any computer and any email client or Web browser. For example, the user would modify the address from "firstname.lastname@example.org" to "email@example.com" and the message would go to the DidTheyReadIt server, which inserts the bug.
Examples of email tracker services are DidTheyReadIt (www.didtheyreadit.com), MSGTAG (www.msgtag.com) and ReadNotify (www.readnotify.com).
A Tracker Notification
This response came from the DidTheyReadIt email tracking service (www.didtheyreadit.com). It was sent back to the sender to inform him that the recipient had opened the mail.