Alan Freedman -- The Computer Language Company - Computer Desktop Encyclopedia
Computer Desktop Encyclopedia
Longest-Running Tech Reference on the Planet

A CDE Definition

You'll love The Computer Desktop Encyclopedia (CDE) for Tech Term of the Day (TTOD)



To be unable to reject the validity of a document (unable to prove it is counterfeit). The term is the opposite of "repudiate," which means to reject the validity of something.

Digital signatures and certificates provide non-repudiation because they guarantee the authenticity of a document or message. As a result, the sending parties cannot deny that they sent it (they cannot repudiate it). Non-repudiation can also be used to ensure that an email message was opened (see email tracker).

email tracker

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 "" to "" and the message would go to the DidTheyReadIt server, which inserts the bug.

Examples of email tracker services are DidTheyReadIt (, MSGTAG ( and ReadNotify (

A Tracker Notification
This response came from the DidTheyReadIt email tracking service ( It was sent back to the sender to inform him that the recipient had opened the mail.

Personal Use Only

Before/After Your Search Term
non-modalnon-routable protocol
non-numeric programmingNon-system disk error or disk error
non-paritynon-text file
non-parity memorynon-tracking browser
non-parity RAMnon trivial
non-PoE devicenon-volatile
non-preemptive multitaskingnon-volatile DRAM
non-procedural codenon-volatile memory
non-procedural languagenon-volatile RAM

Terms By Topic
Click any of the following categories for a list of fundamental terms.
Computer Words You Gotta KnowSystem design
Job categoriesUnix/Linux
Interesting stuffPersonal computers
InternetIndustrial Automation/Process Control
Communications & networkingAssociations/Standards organizations
HistoryDesktop publishing
ProgrammingHealthcare IT
System design