Unsubscribe link injected automatically

Manual unsubscribe link inclusion means that any template published without that link violates CAN-SPAM and GDPR Article 21 simultaneously. In 2024, Gmail and Yahoo added a hard requirement for List-Unsubscribe-Post headers on all bulk sends — without it, messages are increasingly routed to spam or rejected outright. Relying on individual template authors to remember the link is the systematic failure mode: teams under deadline drop it, new contributors don't know the requirement exists, and automated campaign cloning propagates the omission silently.

Inject the unsubscribe footer HTML and both required headers automatically in the ESP adapter layer, keyed on message.emailType, in lib/email/providers/sendgrid.ts:

const isMarketing = message.emailType === 'marketing'
const unsubUrl = isMarketing
  ? `${process.env.APP_URL}/unsubscribe?token=${message.unsubscribeToken}`
  : undefined

await sgMail.send({
  ...basePayload,
  html: isMarketing
    ? message.html + `<p style="font-size:12px"><a href="${unsubUrl}">Unsubscribe</a></p>`
    : message.html,
  headers: isMarketing ? {
    'List-Unsubscribe': `<${unsubUrl}>`,
    'List-Unsubscribe-Post': 'List-Unsubscribe=One-Click'
  } : {}
})

Transactional emails must be explicitly typed so they are not injected; the adapter, not the template author, owns this responsibility.