Email deliverability and DMARC DMARC

Why it matters

Email deliverability is whether your messages reach the inbox rather than spam or nowhere. It depends on your reputation, your content and whether mailbox providers can verify that you are who you say you are. DMARC, defined in RFC 7489, builds on two older checks: SPF (which servers may send for your domain) and DKIM (a signature proving the message was not altered). A DMARC record says what to do with mail that fails both, and asks providers to send you reports.

Since 2024, Google's sender guidelines have required more. All senders need SPF or DKIM and should keep spam rates reported in Postmaster Tools below 0.3 percent. Senders of more than 5,000 messages a day to Gmail accounts need SPF, DKIM and DMARC, one-click unsubscribe for marketing messages, and a spam rate below 0.30 percent. Google's guidance is to aim for below 0.10 percent.

How to set it up

1. List everything that sends as your domain: your mailbox provider, newsletter tool, CRM, billing system.
2. Publish SPF and DKIM for each of them, following that provider's instructions.
3. Add a DMARC record as a DNS TXT record at _dmarc.yourdomain.com, for example v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com.
4. Read the reports for a few weeks and fix legitimate senders that fail.
5. Tighten the policy from none to quarantine, then reject, once real mail passes.

Common mistakes

• Stopping at p=none. It monitors but does not protect.
• Jumping straight to reject and blocking your own invoices.
• Authenticating but sending badly. Unwanted mail, stale lists and no unsubscribe still damage reputation.
• Forgetting forgotten tools, such as an old survey app.

Authentication is the foundation of every email marketing programme BridgeE runs.