Email deliverability

Deliverability is the odds that an accepted message reaches the inbox rather than spam or a bounce. Fabric accepts and sends your mail; whether it lands depends mostly on authentication, reputation, and content — which you control.

Authenticate first

Nothing else matters until SPF, DKIM, and DMARC pass and align with your visible from domain. See Domains & DNS. Unauthenticated mail is the single most common reason a message is filtered or rejected outright.

Send the right mail

• Keep transactional and marketing streams separate. Mixing a promotional blast with receipts on the same domain drags your transactional reputation down with it.
• Always include a plain-text part. Supplying both text and html improves scoring and gives clients a fallback.
• Send to addresses that expect you. Only mail recipients who gave consent; a spike of unknown or invalid recipients looks like spam to receivers.

Watch the signals

• Bounces — a message that a receiver rejects. Retrieve the EmailMessage and branch on its errorCode; stop sending to a hard-bouncing address.
• errorCode — stable and machine-readable. Log it with your business reference, never the recipient content.
• Volume ramp — a brand-new domain has no reputation. Increase live volume gradually rather than sending your entire list on day one.

Verify in sandbox

Sandbox uses a fake provider, so you can exercise the full send → retrieve → webhook loop and your bounce handling with deterministic outcomes before any real inbox is involved. Wire up your consumers there, then authenticate a domain and ramp live volume.

Reputation is per-domain

Deliverability follows the authenticated sending domain, not the API. Protect it: authenticate, send wanted mail, and react to bounces quickly.