TL;DR
Email deliverability is the ability of your emails to land in the recipient's inbox (not spam). It's determined by your domain reputation, authentication records (SPF/DKIM/DMARC), sending behavior, list quality, and engagement metrics. Poor deliverability makes excellent copy worthless.
Deliverability is the unsexy foundation that makes or breaks cold email. You can have the best copy in the world — if it's landing in spam, it's not working.
What determines deliverability:
1. Domain reputation — built over time based on sending behavior. Fresh domains have no reputation (neutral, but suspicious). Old domains with consistent legitimate email are trusted. Burned domains are blocklisted.
2. Authentication records: - SPF: Tells receiving servers which IPs are authorized to send mail from your domain - DKIM: A cryptographic signature that proves the email wasn't altered in transit - DMARC: Policy that tells receiving servers what to do with messages that fail SPF/DKIM All three must be correctly configured. Use MXToolbox to verify.
3. Sending behavior: - Volume ramp-up (warming) - Consistent daily volume (don't spike then disappear) - Sending speed (not blasting 1,000 emails in 5 minutes) - Ratio of new vs. established contacts
4. List quality: - Bounce rate: Must be below 3%. High bounces signal bad list management. - Spam complaints: Must be below 0.1% (Gmail threshold). Too many complaints burns the domain. - Engagement: Emails that get opened and replied to build positive reputation
5. Email content factors: - HTML vs. plain text (plain text delivers better for cold outbound) - Link heavy vs. linkless (links, especially redirects, trigger spam filters) - Spam trigger words - Image-to-text ratio
Tools to monitor deliverability: - Google Postmaster Tools (free, shows your domain's Gmail reputation) - Instantly/Smartlead dashboards (built-in deliverability scoring) - Mail-Tester.com (send a test email, get a spam score) - GlockApps (shows inbox vs. spam placement across all major providers)
From Cactus: Cactus audits deliverability infrastructure before starting any cold email engagement — we've seen too many clients waste budget on campaigns that were landing in spam before we fixed the foundation.
Cactus Marketing embeds with B2B tech startups to turn strategy into pipeline. We've worked with 60+ companies, supported 12 exits, and contributed to $7B+ in client valuations.
Book a free 30-minute call — we'll give you a concrete plan for your situation.
Book a free strategy call →How do I write a cold email that gets replies?
Write one sentence that's specifically about them, one sentence on their problem, one on your solution, and one CTA. The email should be under 80 words, reference something real about their company, and ask a yes-or-no question at the end.
How do I find leads for cold email?
Start with Apollo.io or LinkedIn Sales Navigator to build a list from your ICP criteria. Enrich it through Clay or a waterfall of data providers for verified emails. Target trigger events — recent funding, new hires, job postings — to catch companies in active buying moments.
What is a good cold email reply rate?
A good cold email reply rate is 3–8% for a broad ICP campaign and 8–15% for a highly personalized, trigger-event-based campaign. Anything above 15% with meaningful volume is excellent. Below 2% means something fundamental is wrong — ICP, targeting, or the email itself.
How many cold emails should I send per day?
New domains should warm up for 2–4 weeks before sending real campaigns, starting at 10–20 emails/day and capping out at 30–50/day per domain for sustained campaigns. With multiple warmed domains running in rotation, total volume can reach 500–2,000+/day without domain damage.