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Tags & metadata

tags is a flat map of string key/value pairs attached to a send:

{ "tags": { "campaign": "launch", "plan": "pro" } }

Tags come back on the email object, and you can slice by them everywhere:

  • Filter the list: GET /emails?tag=campaign (any value) or GET /emails?tag=campaign:launch (exact value).
  • Aggregate stats: GET /stats/emails?tag=campaign:launch scopes the whole stats time series to matching sends.

Custom SMTP-style headers are separate: they’re written into the outgoing message itself (e.g. X-Entity-Ref), while tags stay platform-side metadata.

Tags vs data

Section titled “Tags vs data”

When a send includes structured data, that’s what fills template variables, and tags are purely metadata. Without data, tags double as simple flat {{variables}}. Prefer data for templating and keep tags for labeling.