A return receipt, as it relates to computers, refers to the ability for the sender of an email to receive notification back with a date and time stamp of when the recipient opened the mail. A sender might want a return receipt as a matter of course to be sure that all email is actually reaching its destination, or some might only opt for notification when the mail is related to legal or professional matters that require a forensic record. In all cases, the recipient can block generation of a return receipt, purposely or accidentally.
Today's email clients feature a control to request return receipts for mail you send, and a separate control to accept or deny receipts requested of you. First, let’s consider requesting a return receipt.
While it might sound handy to know when people opened your mail, there are a couple of things to consider. First, some people consider return receipts an invasion of their privacy. They prefer to read and answer mail without a “return receipt time clock ticking.” Secondly, if you send a lot of email you could end up with return receipts bombarding your mailbox. This can be overwhelming, though some email clients handle receipts better than others, allowing notifications to be automatically archived with the original mail.
In any case, just because a return receipt is requested does not mean it will be granted. This brings us to the second control mechanism – the ability to accept or to deny return receipt requests.
If the email client is configured to accept return receipt requests, opening an email might generate a pop-up asking for permission to send the notification. Clicking “OK” will automatically generate the time stamped mail without further involvement. Some people, however, are so used to closing pop-up advertisements they might automatically click “No” or “Close” without even reading the window, thereby accidentally denying the receipt.
In other email clients if the return receipt control is left enabled, the program will generate receipts silently in the background without any user interaction. In many cases, this control is enabled by default, and people are unaware their email client is sending out return receipts.
If the email client is configured to deny return receipt requests, they will not be generated. They might still be delivered in a more clandestine fashion, however, through the use of Web bugs embedded in HTML-enabled email interfaces.
What is an HTML-enabled email interface? HTML is the markup language used on the Web. While email was originally designed to be text-only, email clients today can operate in two modes: text only or HTML. Many people choose the HTML-enabled interface because it’s flashier, allowing for embedded Web pages, sounds and images to be viewed inside email messages. It basically amounts to visiting the Web from inside the email client.
Since it is well known that many people choose to disable return receipts, yet use HTML-enabled email interfaces, some companies offer a service to get around disabled receipts. This method requires that the recipient be using HTML style mail, and that he or she has an open link to the Internet at the time the mail is opened. If both these conditions are met, the return receipt is generated via a Web bug.
A Web bug is embedded in the email as a tiny, invisible image holder. When the mail is opened by the recipient, the image holder demands the email program contact the website to download the image. Assuming the computer is online, the website is contacted and the invisible image is downloaded. The image itself is a few transparent pixels, unnoticeable to the reader, but the process trips the return receipt function at the website that is hosting the Web bug. An automatic script generates a time stamp of when the image was requested, and sends a return receipt email to the client. If all goes as planned, the reader never realizes he or she has just tripped a process that generated a return receipt.
Purists tend to configure their email clients to use text-only, as it is more secure than HTML-enabled email. Others opt for HTML mail but configure their email client to block embedded images to avoid arbitrarily downloading Web bugs, viruses, or other malicious scripts. However, this also means blocking legitimate images in many cases. People who use Web-based email (websites that offer email services) might not have a choice, though some services offer the option to block Web bugs.