Woah, Hold on There! What’s All This ‘Image Caching’ About?

Ok, I’ll take it from the top. Traditionally, when you download the images in an email, a request is sent from your email client to an image server. The images are then downloaded in real time from the server and to your email client. Ta-da! Your email is brimming with lovely image-y goodness. Every time the email is opened, this process is repeated.

Under the new Gmail image caching system however, things are a bit different. When you view an email in the Gmail web-interface, a Gmail server acts as an intermediary (what’s known as a ‘proxy’ server) and downloads the images on your behalf. These images are then stored by Gmail in their image cache, so if you open the same email in the future, the images are downloaded from the cache and not the email’s image server.

Got It, so What Does This Have to Do with Tracking Opens?

The way we track and monitor opens is by placing a tiny, invisible image in every email we send. This image is unique to the email in which it’s contained, so when a request comes in to download it, we know which email is being opened.

(Quick fact: Ever wondered why your email client blocks images? It’s to stop spammers using this technique to verify that your email address is active.)

So the Gmail Cache Breaks This?

Not completely. The first email open still downloads the tracking image from an image server, so the open is counted. However, subsequent email opens will be downloaded from the Gmail image cache, effectively breaking this link.

Woah! Will This Affect Campaignmaster Open Tracking?

Nope! We’ve devised a fix that keeps your email open tracking working the same way as it did before. This includes both unique and gross opens.

Gurjeet Dhillon, Managing Director of Campaign Master (UK) Ltd comments;

“Campaignmaster provides three versions of their email marketing product and depending on your package some clients are not affected at all and for others the fix is already in place and is currently being rolled out to the rest of our clients. We expect this fix to be in place for everyone by 18th December 2013. Having said that, don’t panic! The first ‘open’ of all emails will still be recorded in your reporting. However, subsequent opens of the same email may not be fully recorded at this time until the fix is applied and this may be the same for other ESPs.”


From Monday 18th December 2013, the roll-out of our Gmail cache tracking fix will be complete on all Campaignmaster products.

The reason for this change was initially a bit of a mystery, but Google have since announced that Gmail will start displaying images in messages by default. This means no more selecting ‘download images’ on an email.

This is actually a big plus for tracking opens. Previously, if a subscriber viewed your message without downloading images, the open would be ‘lost’. But now, all of these opens will be tracked. Data lovers rejoice!

There are a few other implications of the Gmail caching system, but none of these will affect any Campaignmaster services.

Over the last few days you may have heard about Google’s new ‘image caching’ for Gmail, and the effects that it’s having on some ESPs ability to track multiple ‘opens’ of an email.