Email deliverability

1. Add & verify your domain in Resend

Before anything else, add your sending domain in the Resend dashboard (Domains → Add Domain). Resend generates a set of DNS records unique to your domain — you copy those into your DNS provider (Cloudflare, Namecheap, Route 53, etc.), then click Verify. Send from a subdomain like mail.yourdomain.com or send.yourdomain.com so your root domain's reputation stays independent.

Open Resend → Domains

2. SPF — authorize who can send

SPF (Sender Policy Framework) is a TXT record listing which servers are allowed to send mail for your domain. Resend gives you an SPF (or MX + SPF) record to add. It looks roughly like:

Type:  TXT
Name:  send  (or the subdomain Resend shows)
Value: v=spf1 include:amazonses.com ~all

Gotcha: a domain may have only one SPF record. If you already send through another provider, merge the include: mechanisms into a single record rather than adding a second SPF line.

3. DKIM — cryptographically sign your mail

DKIM (DomainKeys Identified Mail) attaches a signature that proves the message wasn't tampered with and really came from your domain. Resend provides one or more CNAME (or TXT) records — add all of them exactly as shown:

Type:  CNAME
Name:  resend._domainkey  (Resend shows the exact host)
Value: <the target Resend gives you>

Don't let your DNS provider append the domain twice (some auto-add it to the Name field). DKIM is the single most important record for inbox placement.

4. DMARC — set a policy & get reports

DMARC tells receiving servers what to do when SPF/DKIM fail, and where to send aggregate reports. Add a TXT record on _dmarc.yourdomain.com. Start relaxed, then tighten:

Type:  TXT
Name:  _dmarc
Value: v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com; fo=1

• p=none — monitor only (start here for a week or two).
• p=quarantine — send failures to spam once you've confirmed alignment.
• p=reject — the goal: reject unauthenticated mail.

Gmail and Yahoo now require a DMARC record for bulk senders, so don't skip this one.

5. Verify everything

• In Resend, the domain should show a green Verified status once DNS propagates (can take up to ~48h, usually minutes).
• Send a test to mail-tester.com for a 0–10 spam score with a per-record breakdown.
• In Gmail, open a received test → Show original → confirm SPF, DKIM, and DMARC all say PASS.

6. Inbox-placement pitfalls

• No plaintext part. Always send a multipart email (HTML + text). PhluentLabs already does this.
• Spammy content. Avoid ALL-CAPS subjects, excessive !!! , link shorteners, and image-only emails.
• Missing unsubscribe. A visible unsubscribe link (and a list-unsubscribe header) is required for bulk mail — ours is built in.
• Sending to stale lists. High bounce/complaint rates tank reputation. Use double opt-in (the default here) and prune hard bounces.
• Cold domain. Never blast a brand-new domain — see warm-up below.

7. Warm up a new domain

Mailbox providers distrust sudden volume from an unknown domain. Ramp gradually over 2–4 weeks: start with your most-engaged subscribers (recent confirms, frequent openers) and grow volume steadily, watching bounce and complaint rates. Consistent cadence and strong early engagement build reputation faster than raw volume.