Cold email deliverability: the fundamentals

If your email lands in spam, nothing else matters. Subject lines, copy, targeting — irrelevant. Before you optimize anything else, you need the deliverability fundamentals in place.

The three records that gate your domain

Every cold-sending domain needs three DNS records configured correctly:

SPF  — "Who is allowed to send mail on behalf of this domain?"
DKIM — "Cryptographic signature proving the message wasn't altered."
DMARC — "What should receivers do when SPF/DKIM fail?"

Skip any of these and inbox providers will treat your messages as suspicious by default. To see where your domain stands, run it through our SPF, DKIM & DMARC checker.

Domain warmup

A brand new domain has zero sender reputation. If you start sending 200 cold emails on day one, you’ll be flagged immediately. The fix is gradual ramp-up:

Week	Daily volume	Reply rate target
1	5–10	30%+
2	20–30	25%+
3	50	20%+
4	100	15%+

Most warmup tools simulate this with automated reply networks. We’re skeptical of those — providers have gotten good at detecting them. Warming with real conversations (internal team, friendly customers) is slower but durable.

What actually moves deliverability

After ten years of watching this space, the things that consistently matter:

1. Use a separate domain for cold outbound. Don’t risk your primary corporate domain.
2. Cap volume — under 50/day per inbox is the modern conservative number. Our inbox and domain calculator works out how many inboxes that means for your volume.
3. Monitor bounce rate — anything over 5% and you stop sending immediately, then paste the bounces into our SMTP error code lookup to tell bad addresses from blocks.
4. Watch reply sentiment, not just reply rate. A 20% angry-reply rate will burn you faster than 0% replies.

The teams that get this right rarely think about deliverability. The teams that don’t, think about nothing else.