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.
A campaign using the Gmail backend is the one exception: it sends from a connected Gmail / Workspace mailbox that authenticates itself, so it needs no verified domain. Everything else below (suppressions, quotas) still applies.
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.