What is remote content blocking?

Remote content blocking is what happens when an email client doesn't automatically load external images, tracking pixels, or other resources hosted outside the email itself. Instead, the reader sees placeholder boxes with "Display images" or "Show pictures" prompts.

Every major email client (Gmail, Outlook, Apple Mail, Yahoo Mail) does this by default for new senders or unfamiliar domains. The reason: privacy. When you load a remote image, the sender learns your IP address, that you opened the email, what time you opened it, and what device you used. Clients block that automatic handshake until the reader chooses to trust the sender.

This is why open tracking isn't 100% accurate. Most email platforms track opens by embedding a tiny 1x1 pixel image at the bottom of your email. If the client blocks remote content, that pixel never loads, so the platform never knows the email was opened. (Some readers disable image loading permanently, which means they'll never show up in your open stats even if they read every word.)

For senders, remote content blocking means your email design needs to work with images off. Always include alt text so readers know what they're missing. Write meaningful copy in the email body, not just image-based CTAs. And don't panic when your open rate looks low for a new campaign. A 20% measured open rate might actually be 35% if you account for blocked tracking pixels.

Want to see how your email looks with images blocked? Send yourself a test and disable remote images in your inbox settings before opening it. If the email is unreadable or the CTA is invisible, fix that before you send to your list.