Tagging your Pepipost emails lets you easily search activity, compare stats, and more. Some examples of Tags are: "Invoice Emails", "Forgot Password/OTP", "Newsletters" etc. Add tags to emails while sending emails through API or SMTP.
In case of SMTP just add an additional header to each of your emails:
X-TAGS: "Forgot Password";
You can have multiple comma separated tags assigned to the same email.
Here is one example:
X-TAGS: "Movie Tickets, Invoice Emails";
Once the Tags are assigned to emails, you can analyze the same under your Pepipost account.
The X-TAGS that you add will be stripped from the final email because they are headers for internal tracking purpose. So you can expect to not actually see these headers in the final email.