Email Deliverability

Why deliverability matters, what Defrost does for you automatically, and what you have to set up yourself (DNS + warmup).

Why this matters

A cold email that lands in spam might as well not have been sent. The difference between a healthy 30% reply rate and a campaign that fizzles to 1% is almost always deliverability — not copy, not targeting, not timing.

Defrost protects deliverability with three mechanisms: DNS authentication (you set up once), warmup (we run automatically), and send-time safety limits (always on).

DNS authentication — set up once

Mailbox providers (Google, Microsoft) ignore mail that fails authentication. You must publish three DNS records on your sending domain:

  • SPF — tells the world which servers are allowed to send on behalf of your domain
  • DKIM — cryptographic signature proving the email wasn't tampered with in transit
  • DMARC — tells receivers what to do when SPF or DKIM fails (we recommend p=quarantine to start)

Defrost checks these records and shows red/green status under Settings → Domains. If any record is missing or misconfigured, the page tells you exactly what to add and where to add it.

Most DNS providers (Cloudflare, Namecheap, GoDaddy, Squarespace) let you add records through their dashboard. Propagation usually takes 15 minutes to a few hours.

Warmup — automatic, but takes time

A brand-new mailbox cannot send 50 cold emails on day one. Mailbox providers track sending reputation; new accounts get scrutinized hard. Warmup gradually ramps the volume so providers learn to trust you.

Defrost's warmup engine sends and replies to seed addresses on your behalf following an industry-standard ramp curve:

  • Day 1: ~5 sends/day
  • Day 7: ~15 sends/day
  • Day 14: ~30 sends/day
  • Day 30: ~50 sends/day (full volume)

The ramp adapts: if reputation drops (bounces, complaints, low open rates), warmup slows. Once a mailbox shows 30 days of clean performance, you can opt into faster ramps for additional accounts.

Send-time safety limits

Even with DNS + warmup in place, Defrost enforces hard ceilings at send time:

  • 50 emails/day per warm mailbox (20/day for warming accounts)
  • 30 emails/hour per recipient domain (so a 500-lead campaign at @acme.com can't burst-send)
  • 45-120 second random delay between consecutive sends from the same mailbox
  • 5% bounce-rate threshold — exceeding it auto-pauses the campaign and alerts you

These limits exist to keep you below the radar of mailbox providers' rate-limiters and abuse heuristics.

What to do when bounces spike

If you see bounces above 3%:

  1. Pause the campaign (Defrost auto-pauses at 5%, but pause early manually)
  2. Check Settings → Mailboxes — is there a sudden reputation drop?
  3. Check Settings → Domains — did a DNS record change?
  4. Inspect the bouncing leads — are they stale or from a low-quality source?

If you exhaust those, the Troubleshooting page covers deeper diagnostics.

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