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, for how long, 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:
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.
If a user views emails in a client that blocks images from loading, Postmark can't track opens for those emails.
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.
Postmark stores the information about individual opens for 45 days. Aggregated statistics are stored forever.