User guide

API reference


Tracking opens

What is open tracking? #

Sending emails with open tracking enabled will embed an invisible pixel into your emails that allows Postmark to record information when the email is viewed. Postmark handles the job of embedding the pixel and saving all of the information associated with the request. For every email you send and for each recipient you send to, you can see if your emails are getting read, in what environments, and more. When Postmark saves open tracking information, we save the information as a unique open, aggregated by the tag you sent the email with, and aggregated for your account overall.

With the data provided by open tracking, you can get some new insights into your business:

  • Individual open tracking—My user Jane hasn't opened any emails this month, maybe she isn't an active user any more? 
  • Tracking opens by tag—Sending emails with an exclamation point in the subject results in two times the opens!
  • Geographic information—20% of my emails are being read in Mexico, should I translate my app into Spanish?
  • Email client—A majority of my emails are being read in Outlook, I should make sure my email designs look great there.
  • Platform—Most of my users are reading emails on mobile devices, I need to get the mobile version of my site ready ASAP!
  • Operating system—Only 2% of my users are reading emails on a Mac, maybe I don't need to invest in an OSX desktop application.

Limitations #

HTML only

We can only add a tracking pixel to HTML emails. If you send plain text only emails or if a user only reads the plain text version, Postmark can't track opens for those emails.

Blocked images

If a user views emails in a client that blocks images from loading, Postmark can't track opens for those emails.

Ad Blockers

Ad Blockers may interfere with tracking opens, if the users setup has blocked the tracking pixel URL.


Using the Gmail website and mobile applications will display images served through a proxy server. This means that Postmark will be able to detect when an open occurs for Gmail users. However, we won't be able to detect geography, operating system, and some other information.

Apple Mail

Starting in iOS 15, Apple allows iOS users using Apple Mail to turn on a setting called Mail Privacy Protection that can cause false-positive opens to be reported.

Individual open storage

Postmark stores the information about individual opens for 45 days. Aggregated statistics are stored forever.