Sends email with the project sending token (x-lettermint-token).

Every function needs :sending_token on the client. Nothing about a message is stored on the client: every call sends exactly what it is given.

lettermint = Lettermint.new(sending_token: System.fetch_env!("LETTERMINT_PROJECT_TOKEN"))

{:ok, result} =
  Lettermint.Emails.send(lettermint, %{
    from: "Acme <hello@acme.com>",
    to: ["jane@example.com"],
    subject: "Welcome",
    html: "<p>Thanks for signing up.</p>"
  }, idempotency_key: "welcome-jane")

A message is a map in the API's field names (reply_to, scheduled_at, sandbox_result, ...) with atom or string keys, or a Lettermint.Types.SendMailRequest struct. For the pipe-friendly builder, see compose/2 and Lettermint.EmailBuilder.

Attachments

An attachment is a map with :filename, :content, and optionally :content_type and :content_id. content is base64 text, as the API expects it, or {:bytes, binary} with the raw bytes, which the SDK base64-encodes:

attachments: [
  %{filename: "invoice.pdf", content: {:bytes, File.read!("invoice.pdf")}, content_type: "application/pdf"},
  %{filename: "logo.png", content: logo_base64, content_id: "logo"}
]

Tags

tags holds up to 20 name/value tags (19 when the legacy tag is also set). Names match ^[A-Za-z0-9_-]{1,32}$, must not start with __lettermint and must be unique (case-sensitive); values match ^[A-Za-z0-9_-]{1,64}$. The SDK checks this before the request and returns Lettermint.ClientValidationError.