Cold Email Deliverability: How to Land in the Inbox, Not Spam

Gmail, Outlook, and the rest score every sender on signals: is the domain authenticated (SPF, DKIM, DMARC), does the sending history look like a real person (volume, consistency, bounce rate), and do recipients actually engage (opens, replies, spam complaints)? The score is compared against the sender's baseline — a sudden spike in volume or bounces trips the alarm regardless of your absolute numbers.

• SPF: publish which servers are allowed to send from your domain.
• DKIM: sign outgoing mail so receivers can verify it wasn't forged.
• DMARC: publish a policy — start with monitoring (p=none), then move to quarantine/reject once SPF and DKIM are stable.
• Separate domains: send cold outreach from a dedicated subdomain (outreach.yourdomain.com) so a misstep never tanks the domain you use for real customer mail.
• Verified sending platform: your tool should let you confirm all three records and warn you when they're missing.

• Warm up gradually: start at 10–30 emails a day and scale over 2–4 weeks, letting engagement signals accumulate before you raise volume.
• Cap daily volume: even warmed up, most providers stay safest under ~200/day per mailbox; hundreds more need multiple mailboxes and split domains.
• Match sending to replies: reply to every positive and negative response quickly — engagement is the strongest reputation signal there is.
• Consistent schedule: a steady 80/day beats 400 on Monday and zero the rest of the week.
• Slow down for new domains: a fresh domain has zero history — treat its first month as a probation period.

• Image-only emails: no text for spam engines to read.
• Link-heavy bodies: more links than words reads like a blast.
• Attachment spam: PDFs and ZIPs on cold email are a classic malware pattern.
• Spam vocabulary: 'free', 'guaranteed', 'act now', '100%', excessive caps and exclamation marks.
• Fake headers: 'Re:' or 'Fwd:' subject lines and forged display names get flagged fast.
• Unsubscribe trap: an email without a working unsubscribe violates law in most markets and earns complaints.

• Bounce rate under 2%: verify addresses before sending and purge hard bounces immediately — a spike is the fastest way to get blocked.
• Spam complaints under 0.1%: one complaint per thousand sends is the ceiling most providers tolerate.
• Reply rate over 3%: replies are the strongest engagement signal; below that, question the list and the angle, not just the subject line.
• Blacklist checks: watch the major blocklists monthly — a listing explains sudden drops to zero.
• Warmup recovery: if reputation slips, drop volume, clean the list, and let engagement rebuild before scaling again.

None of this makes a bad email good — it makes a good email reachable. The deliverability checklist is the toll booth on the way to replies; what you say once you're in the inbox still decides whether anyone answers.