How email tracking works
The Altcraft platform tracks recipient engagement with email messages using invisible tracking pixels. Based on pixel loading data, the platform generates metrics for opens, glances, skims, and reads.
Whenever possible, place tracking pixels closer to the beginning of the email. This ensures that the email client loads them sooner and reduces the risk that Gmail clipping will prevent an open from being recorded. However, the pixels must be carefully embedded in the HTML template so that they do not affect the email layout.
Tracking mechanism
Two invisible 4×4 pixels are automatically added to each email:
- Open pixel — placed at the end of the email. When this pixel loads, the platform records an email open event. If the pixel does not load (for example, images are blocked), the open may be registered on the first click on a link within the email.
- Read pixel — placed after the main content. When this pixel is requested, the server keeps the HTTP connection open for up to 12 seconds and measures how long the mail client holds the connection.
Based on the HTTP connection duration, the event type is determined:
| Event type | Name | Duration |
|---|---|---|
| Glance | Glanced | 0–4 seconds |
| Skim | Skimmed | 4–8 seconds |
| Read | Read | 8+ seconds |
If the connection is closed before 12 seconds (for example, the recipient closed the email), the actual viewing time is recorded and the corresponding event type is registered. The maximum wait time is 12 seconds: if the email stays open longer, the server closes the connection and registers the event as a read.
Email client limitations
Not all email clients load tracking pixels correctly. Below are the main scenarios where metrics may be incomplete or missing.
Remote image blocking
Some email clients block remote content by default, including tracking pixels:
- Outlook — remote content blocking is enabled by default. The user must manually click "Download Images" for each email.
- Thunderbird — image blocking is enabled by default.
- Yahoo Mail — may block remote content.
Consequence: pixels do not load, opens and reads are not recorded.
Solution: add the platform's tracking domain to the image blocking exceptions.
Image proxy servers
Some email services do not load images directly from the sender's server, but through their own proxy:
- Gmail Image Proxy — all images in emails are loaded through Gmail's proxy. The pixel is opened, but the HTTP connection is closed immediately after loading, so the viewing time is zero.
- Apple Mail Privacy Protection (MPP) — images are loaded through Apple's proxy with randomized timing. The open is recorded, but the viewing time does not reflect the user's actual behavior.
- Corporate proxies (Proofpoint, Mimecast, etc.) — similar to Gmail's proxy, load pixels through an intermediate server.
Consequence: the open is recorded, but glanced/skimmed/read metrics do not work — the proxy does not keep the HTTP connection open, so timeload ≈ 0 and only a glanced event with zero is registered.
Gmail prefetching
Gmail may pre-load images from emails even if the recipient has not opened the email — for example, when displaying in the preview pane or when indexing content.
Consequence: a false open is recorded, even though the email was not actually viewed.
Gmail clipping
Gmail may truncate long emails, removing part of the content, including tracking pixels, if they are located beyond the truncated area.
Consequence: the pixel does not load, the open is not recorded.
Why glanced/skimmed/read may not be recorded
The glanced/skimmed/read metrics are based on measuring the HTTP connection duration when loading the read pixel. This mechanism works only with a direct connection between the mail client and the tracking server.
When the request goes through a proxy server:
- The proxy loads the pixel on behalf of the client
- The proxy saves the image and delivers it to the client
- The HTTP connection between the proxy and the tracking server closes immediately after loading
- The server records
timeload ≈ 0and registers a glanced event
Thus, glanced/skimmed/read metrics work only with a direct connection without a proxy. Through a proxy, the only reliable signal is the open event (request received or not).
Recommendations
How to check if a client blocks images
Send a test email to your own address and open it in the problematic mail client. If the report does not record an open, the client blocks remote images or uses a proxy.
How to add the tracking domain to exceptions
Find out from the platform administrator which domain is used for tracking. Add this domain to your mail client's exceptions list:
- Outlook: allow automatic image loading or add the domain to trusted senders (the exact path depends on your Outlook version).
- Thunderbird: Settings — Privacy — Uncheck "Warn me when web sites try to load images".
- Apple Mail: Settings — Privacy — Uncheck "Load remote images through proxy".
Which metrics to rely on when working through proxies
If most of your audience uses email services with image proxying (Gmail, Apple Mail), the glanced/skimmed/read metrics will be incomplete. In this case, it is recommended to focus on:
- Opens — a "yes/no" metric that works even through proxies.
- Clicks (CTR) — do not depend on tracking pixels, reflect real engagement with content.
- CTOR — the percentage of clicks from opens, shows engagement among those who opened the email.