Categories help organize your email analytics by enabling you to tag emails you send by topics you define.
The events that can be associated with category include:
The actual statistics included vary depending upon the set of enabled apps. Emails sent, bounces and spam reports will always get tracked. Unsubscribes, Clicks, and Opens require that the associated Setting is enabled. Check out Settings to see which apps you have enabled.
In order to add the X-SMTPAPI categories header, please look at our SMTP API Categories) documentation. You can also get a full category list or get category specific statistics from the SendGrid API.