How Are Emails Detected as “Viewed”?

Overview

Emails are often tracked to determine when a recipient has opened or viewed them. The most common technique used for this purpose is pixel tracking — a small, invisible image embedded in the email that signals when the message is opened.

How It Works

Embedding a Tracking Pixel

A tiny, transparent image (typically 1×1 pixel) is inserted into the email body, for example:

<img src="https://yourdomain.com/track/open?id={email_id}" width="1" height="1" style="display:none;" />

This image is hosted on a tracking server.

When the Email Is Opened

When the recipient's email client loads the message and its images, it automatically requests the tracking pixel from your server.

Recording the Event

Each request to the pixel endpoint can be logged with metadata such as:

• Email ID or campaign reference
• Timestamp of open
• IP address and device information (if applicable)
• User agent (browser or email client)

This information is stored to mark the email as "viewed" or "opened."

Limitations

Image Blocking

Many email clients block remote images by default, meaning the pixel may not load until the user allows images.

Privacy Restrictions

Regulations like GDPR and CCPA limit the collection of identifiable data without user consent.

Partial Visibility

If the user previews the email without loading images, it may not register as opened.