Concepts

Transactional vs marketing

• Transactional (X-Md-Channel: trans): 1:1 email triggered by user actions (confirmations, OTP, receipts). High deliverability expected.
• Marketing / bulk (X-Md-Channel: bulk): list campaigns, drip (sequences). Subject to suppressions and unsubscribes.

Sending domains

You can only send from verified domains associated with your account. Verification publishes SPF/DKIM/DMARC; DKIM signing is handled by the platform via CNAME delegation (you publish a CNAME once and we rotate the key without you touching your DNS).

Reputation and deliverability

Reputation is built per domain + IP. Start with moderate volumes (warmup), keep your bounce/complaint rate low, and respect suppressions.