Deliverability & suppressions
Verified senders, suppression lists, and domain health that protect your reputation.
Guardrails that protect your sending reputation — and what they return when they trip.
Verified senders only
A from address must be on a domain you've verified. Sending from an unverified
address is rejected with 403 forbidden. This prevents one project from sending
as another. Verify domains under Domains in your dashboard.
Suppressions are enforced
Addresses that hard-bounced, marked a message as spam, or unsubscribed are added
to your suppression list. Sending to a suppressed address returns 409 conflict,
and trying to add one as a contact is blocked too. This keeps your bounce and
complaint rates low, which keeps you in the inbox.
Domain health
If a sending domain has an open high-impact deliverability recommendation (for
example a missing DMARC record), sends from it are paused with 403 forbidden
until you resolve it under Domains.
Include a plain-text text part alongside your html on transactional sends.
Multipart messages land in the inbox more reliably and render for text-only
clients.
Each of these maps to a specific error code — see the error reference for how to detect and resolve them.