Changelog

2026-09

Improvements

• CC and BCC — cc and bcc fields now accepted on POST /v1/send. Same format as to (string, {name, email} object, or array). BCC is envelope-only and never written to MIME headers.
• Plain-text MIME part — Every outbound email now includes a text/plain alternative. Supply text explicitly or let Sendbound auto-generate it from the HTML body. Improves deliverability and accessibility.
• html field alias — html is now accepted as an alias for body on /v1/send. Useful when migrating from Resend or SendGrid without changing your payload shape.
• replyTo field alias — replyTo is now accepted as an alias for reply. Useful when migrating from Resend or Postmark.
• RFC 5322 display-name format — "Name <email>" strings are now accepted everywhere an email address is expected (to, from, cc, bcc). Parsed automatically before validation.
• id in send response — POST /v1/send now returns a top-level id field (the email record ID) alongside the existing data.emails array. Matches the response shape of Resend and Postmark.
• Unknown-field warnings — Unrecognised fields in the request body are no longer silently dropped. The response now includes a warnings[] array listing what was ignored, making migration debugging easier.

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2026-01

New features

• SMTP relay — Send transactional email over SMTP on port 587. Authenticate with apikey as the username and your secret key as the password.
• Inbound routing — Receive inbound email at your verified domain and forward it to a webhook endpoint.
• Preference center — Hosted unsubscribe page automatically linked in campaign footers.
• A/B testing — Test up to 5 subject line variants on a campaign before sending to the full audience.
• Warm-up schedules — Automatically ramp sending volume on new domains to build reputation.

Improvements

• POST /v1/contacts now performs an upsert by email address — no more duplicate errors on re-import.
• Webhook payloads now include messageId for correlation with your email provider.
• Campaign stats are now available via GET /v1/campaigns/:id — no separate stats endpoint required.

2025-Q4

New features

• Segments — Dynamic contact segments based on tag, subscription status, or custom data.
• Templates — Reusable HTML templates referenced by ID in campaign and transactional send requests.
• Contact tags — Attach arbitrary string tags to contacts for filtering and segmentation.

Breaking changes

• None. The API remains backward-compatible on the v1 prefix.

2025-Q3

Initial API launch. Core endpoints: /v1/send, /v1/contacts, /v1/domains, /v1/api-keys.