Has Your Email Been Read? Read Receipts and Web Bugs

July 1st, 2020


Customers often ask how they can know if a specific recipient has read a message. Typically, this is done by requesting a “Read Receipt” when sending the message. However, read receipts are unreliable. Spammers use techniques such as HTML “web bug” tracking to see if you have read an email message and thus if your email address is valid and ripe for more spamming; this is also unreliable. LuxSci’s SecureLine Escrow service includes a 100% reliable Read Receipt function that can be used when it is essential to know if someone has read a message. It also allows for message retraction (removing further access to an email message).

This article explains how to determine if a message is read, shows how each method works and discusses the pros and cons.

Read Receipts

Read Receipts are requests attached to an email message by the sender. Most email programs, like Outlook, Thunderbird, and LuxSci WebMail, allow Read Receipts to be added to email messages and allow senders to choose if recepts are sent “never,” “on-demand,” or “always.”

Sending: Read Receipts are implemented by adding a special “Header” to the headers area of the outbound email message (See: Viewing the Message Source / Full Headers of an Email). For example, if somebody@luxsci.net sent an email message and wanted a Read Receipt, the following “Disposition-Notification-To” header would be added:

Disposition-Notification-To: somebody@luxsci.net

Receipt: When the recipient first opens the message, the recipient’s email program may see this header and send a special “Delivery Notification” email back to the address somebody@luxsci.net. When somebody@luxsci.net gets this notification, they know the message has been read.

Not Reliable: Read Receipts are not a reliable way to know if a message has been read. Why?

  • No Support: The recipient’s email program might not support responding to Read Receipt requests. In this case, receipts would never be sent.
  • Refusal: Even if the email program supports Read Receipts, the programs generally allow recipients to choose if they should respond. I.e., recipients could choose to respond “never,” “always,” or “decide each time.” The default usually prompts the recipient and allows them to decide yes or no for each receipt.

So, if you use a Read Receipt to confirm delivery, you will usually only get a receipt if the recipient wants you to. Sending Read Receipt requests is unreliable for confirming the read status of a message in general, especially if the recipient tries to deny that the message was even received!

Web Bugs

So, how can you tell if someone has opened and read a message without a Read Receipt request and without letting the recipient know that you are “checking”?

When an HTML-formatted email message is opened, any referenced external objects such as images are usually downloaded from the internet and displayed. For example, if someone sends you an email message with a link to display a picture of somebody, and that picture is not attached to the message but hosted somewhere (like on Facebook), then your email program will download that image and display it to you.

The trick is for the sender to include some unique tracking code in the link to that picture. Then the picture is downloaded, the web server where it was stored records that download, complete with the date, time, tracking code, and your computer’s IP address. By looking at those web server log files, the sender can confirm if you have downloaded the image and thus if you have read the message.

Typically, but not always, the tracking code is attached to some small innocuous image (like a small invisible image). These small tracking images are collectively known as “web bugs” because your email is “bugged.”

Not Reliable: Web bugs are not a reliable way to know if a message has been read. Why?

  • No HTML: If the recipient opens the message in an email program with HTML support turned off, no images or other objects will be downloaded. For example, LuxSci WebMail shows recipients a plain text preview of their messages. There is no way to track opening the plain text preview of a message using a web bug.
  • Images Off: If the recipient has turned the display of external images off in their email program, then the web bugs would never be downloaded. This is an optional feature in some programs like Thunderbird and LuxSci WebMail.
  • Web Bug Extraction: Some email filters will auto-detect images that look like web bugs (i.e., images that look like tracking codes) and automatically remove them by replacing them with transparent images. In this case, the web bugs would not be downloaded, but other images would show up fine. LuxSci’s Premium Email Filtering can do this.

Spammers don’t care that this is not 100% reliable. It is “good enough” to identify a large number of valid recipients and thus allows them to narrow down their lists and send these people more spam. See Protecting Yourself from Email “Web Bugs.”

Reliable Read Receipts

So, how can you know, 100% of the time, if your recipient has read your message or not?

The only way to do this is to control the recipient’s ability to read the message. A common way to do this is to:

  • Save the message on a website over which you have control
  • Send the recipient a notice that a message is waiting for them on that website and provide them with the means to access it.
  • When the recipient connects and uses their access credentials successfully to open the message, you record that fact.

In this way, you know if and when the message was retrieved. You also know how many times it was accessed, from what IP address(es), and you could remove access to it (i.e., retract it) at any time. These Reliable Read Receipt and Retraction features are included in LuxSci’s SecureLine Escrow service.

Other email systems may also provide reliable ways of Read access tracking; in every case, it depends on:

  • The system is configured to support it, and
  • Having complete control over the system that the recipient uses to access the message

If you do not have access to control your recipient’s email system, you should consider using a message pickup system with tracking included, such as SecureLine Escrow.