The Device and Client tab on the Sent Message Report tells you which devices and email clients your contacts used to open a message. It's built from a tracking pixel that loads when an HTML email is opened, and third-party libraries that identify the device from that signal. When the signal isn't clear, you'll see entries labelled Unknown Device or Default Browser Client.
Why this matters: Device and client data tells you which environments to design and test for. Understanding why some opens show up as Unknown stops you from chasing ghosts in the data, and helps you interpret the parts of the report that are reliable.
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- Device and client are detected from the tracking pixel when a contact opens an HTML email.
- Unknown Device usually means the pixel loaded through an image proxy (Gmail, Apple Mail Privacy Protection, Yahoo).
- Clicks without a pixel load still count as opens but cannot identify device or client.
- New devices and niche clients may not be recognised by the detection libraries yet.
- Bots that aren't on your ignored IP list can also appear as Unknown opens. See False Opt-Outs & Email Clicks.
Try it like this: On any Sent Message Report, click the Device and Client tab. If a large share of opens show as Unknown Device, check whether most of your list uses Gmail or Apple Mail: those providers route images through a proxy, which masks the device.
Why you see Unknown Device or Default Browser Client
There are four common reasons:
- The tracking pixel came through an image proxy. Gmail (including Google Workspace), Yahoo Mail, and Apple Mail Privacy Protection route images via a proxy server. Act-On sees the proxy's signature, not the recipient's device. Read Google's explanation of this behaviour here.
- The contact clicked a link without loading the pixel. A click still counts as an open, but without the pixel there's no device signal.
- The device or client isn't in our libraries. Brand new phones, operating systems, or niche clients can take time to appear in the detection data.
- A bot or scanner loaded the pixel. If the scanning IP isn't on your ignored list, its open is counted without any usable device data. See Ignore Activity from Known IP Addresses to filter these out.
Note: A high Unknown Device count isn't a bug. It usually reflects your audience's mail providers. Use the known-device data for design decisions and treat the Unknown share as the remainder.
What to do about it
You cannot force a device into the known category. However, you can shrink the Unknown share by adding scanner IP ranges to your ignored list so those bot opens drop off. See Ignore Activity from Known IP Addresses and False Opt-Outs & Email Clicks for the full process.