自定义标头

headers 是由字符串键和字符串值组成的对象，会原样写入邮件。

Node.js
cURL

import { SpacePost } from "@spacepost/node";

const spacepost = new SpacePost(process.env.SPACEPOST_API_KEY);

await spacepost.emails.send({
  from: "Acme <hello@acme.com>",
  to: "user@example.com",
  subject: "Weekly digest",
  html: "<p>...</p>",
  headers: {
    "List-Unsubscribe": "<https://acme.com/unsubscribe?u=1042>, <mailto:unsubscribe@acme.com>",
    "List-Unsubscribe-Post": "List-Unsubscribe=One-Click",
    "X-Entity-Ref-ID": "digest-2026-w43-1042",
  },
});

curl -X POST https://api.spacepost.dev/emails \
  -H "Authorization: Bearer $SPACEPOST_API_KEY" -H "Content-Type: application/json" \
  -d '{
    "from": "Acme <hello@acme.com>",
    "to": ["user@example.com"],
    "subject": "Weekly digest",
    "html": "<p>...</p>",
    "headers": {
      "List-Unsubscribe": "<https://acme.com/unsubscribe?u=1042>",
      "List-Unsubscribe-Post": "List-Unsubscribe=One-Click"
    }
  }'

常见用途

标头	用途
`List-Unsubscribe` and `List-Unsubscribe-Post`	一键退订（RFC 8058）。Gmail 和 Yahoo 要求群发发件人必须具备。群发会自动添加。
`X-Entity-Ref-ID`	每封邮件使用唯一的值。可防止 Gmail 把相似的邮件折叠成同一会话，或隐藏页脚。
`In-Reply-To`, `References`	将邮件串联到已有的会话中。
`X-*`	任何应用自定义的元数据。通过 SMTP 发送时，`X-` 标头会被转发，但 SpacePost 自己的 `X-SpacePost-` 控制标头除外。