Cold email deliverability: SPF, DKIM, DMARC & warm-up

Great emails are worthless in the spam folder. Deliverability is the craft of landing in the inbox — and it comes down to a few things you set up once, plus a warm-up you let run.

1. Send from a separate domain

Never send cold email from your main business domain. One spam complaint can hurt the reputation of the domain you use for real customer email. Buy a lookalike domain (e.g. yourbrand-mail.com) for ~$10/year and send from that. If it ever gets burned, your primary domain is untouched.

2. Set up SPF, DKIM and DMARC

These three DNS records tell receiving servers your mail is legitimate. Without them, you go straight to spam.

• SPF — lists which servers are allowed to send for your domain.
• DKIM — cryptographically signs your emails so they can't be forged.
• DMARC — tells receivers what to do if SPF/DKIM fail, and gives you reports.

Every email provider (Fastmail, Google Workspace, Zoho…) has a step-by-step guide — it's three DNS records and about ten minutes, one time.

3. Warm up the inbox before you send at volume

A brand-new inbox that suddenly blasts 200 cold emails looks exactly like a spammer. Warm-up fixes this two ways:

• A daily ramp. Start small and grow the daily cap over weeks. A week-one inbox should send only a handful per day.
• Engagement signals. Exchange normal email with "seed" inboxes that open, mark-as-important, and reply — the positive signals mailbox providers reward.

Doorstep automates both: a configurable ramp per inbox, and a seed-engagement routine that runs daily without you.

4. Protect yourself with a bounce circuit-breaker

A rising bounce rate is the fastest way to wreck a domain. Set a threshold (5% is sensible) that pauses all sending until you clean your list. Doorstep does this automatically and suppresses bounced addresses forever.

5. Keep the emails human

Deliverability isn't only technical. Short, specific, genuinely-relevant emails get replies and few complaints; generic mass blasts get flagged. This is why Doorstep has your own Claude personalize every draft from real business details — and why you approve every send.