The 2026 cold-email deliverability checklist: 17 things to verify before scaling
Comprehensive pre-scale checklist for cold-email infrastructure. Every item is binary - pass or fix - with the dig command or test to confirm.
Rejwan Nirob·May 23, 2026·8 min readCold-email infrastructure at scale lives or dies on the boring details. This checklist covers every layer that matters in 2026 - DNS auth, mailbox config, sending tool, list quality, content. Run through the 17 items before scaling any cold program past 50 mailboxes. Each item is binary: pass or fix.
DNS authentication (items 1-6)
- 1. SPF record present and singular - dig +short yourdomain.com TXT shows exactly one v=spf1 entry
- 2. SPF includes match all sending services - Workspace, marketing tools, etc.
- 3. DKIM record present and 2048-bit - dig +short google._domainkey.yourdomain.com TXT returns long base64
- 4. DMARC published at p=quarantine minimum - dig +short _dmarc.yourdomain.com TXT
- 5. DMARC alignment relaxed (aspf=r adkim=r) - allows subdomain alignment
- 6. MX records pointing at correct provider with all 5 priorities (Google) or equivalent (M365)
Mailbox configuration (items 7-10)
- 7. 2-to-3 mailboxes per domain - never 4+
- 8. Mailbox names match real human pattern - first.last@yourdomain.com
- 9. From name matches mailbox (no spoofing the display name)
- 10. Reply detection configured so engaged recipients drop out of sequences
Sending tool configuration (items 11-13)
- 11. Warmup mode enabled for any mailbox under 14 days old
- 12. Daily send cap at 10 to 20 per mailbox - well below the platform ceiling
- 13. Sending window restricted to Tuesday-Thursday 9-11am recipient local timezone
List quality (items 14-15)
- 14. Every recipient validated within 90 days (ZeroBounce, NeverBounce, MillionVerifier)
- 15. Suppression list applied - every prior unsubscribe persists across campaigns
Content (items 16-17)
- 16. List-Unsubscribe header on every send (Gmail/Yahoo bulk-sender requirement above 5K/day)
- 17. mail-tester.com score above 9.5/10 for the campaign template
Run the test send
After all 17 items pass, send the actual campaign to a controlled seed list of 20 inboxes across Gmail, Workspace, Outlook, and M365. Primary-inbox placement above 70 percent means the infrastructure is ready to scale. Below 70 percent, something is missing from the 17 above - re-audit before scaling.
“Seventeen checks. None of them takes more than a minute. Skip them and you find out which one was failing the hard way - usually with a Spamhaus listing two weeks in.”
The scale-up cadence
After the 17-check pre-flight passes, ramp gradually. Start at 25 percent of target volume for week 1, 50 percent week 2, 75 percent week 3, 100 percent week 4. Monitor Postmaster Tools daily and seed-list placement at every step. A 4-week ramp on a 17-checks-passed stack reliably reaches steady-state without triggering filters.
Inboxlee handles items 1-6 (DNS auth), item 7 (mailbox-per-domain ceiling), item 8 (naming convention) and surfaces items 14, 16, 17 in the dashboard. You handle list quality, sending-tool config, and content. The 17-check pre-flight becomes a 5-check pre-flight on Inboxlee infrastructure.
See infrastructure monitoringFrequently asked
What is the complete cold-email deliverability checklist for 2026?
17 items across 5 categories: DNS authentication (SPF singular, DKIM 2048-bit, DMARC at p=quarantine, MX correct, alignment relaxed), mailbox config (2-3 per domain, real-name mailboxes, no display-name spoofing, reply detection), sending tool (warmup enabled, 10-20/day cap, Tue-Thu 9-11am local window), list quality (validated within 90 days, suppression applied), content (List-Unsubscribe header, mail-tester score above 9.5).
What should I check before scaling a cold-email program past 50 mailboxes?
The 17-check pre-flight in order, ending with a seed-list test on 20 inboxes. Primary-inbox placement above 70 percent on the seed list confirms the infrastructure is ready. Then ramp gradually - 25% volume week 1, 50% week 2, 75% week 3, 100% week 4 - monitoring Postmaster Tools and placement daily at each step.
How do I verify SPF, DKIM, and DMARC are configured correctly with dig?
Three commands. dig +short yourdomain.com TXT (look for v=spf1, exactly one entry). dig +short google._domainkey.yourdomain.com TXT (DKIM key, long base64, 2048-bit). dig +short _dmarc.yourdomain.com TXT (DMARC record at p=quarantine or p=reject, aspf=r adkim=r). All three must return the expected values. Any missing or duplicated entry means fix before sending.
What is the safe ramp rate after a cold-email infrastructure audit passes?
25% of target volume week 1, 50% week 2, 75% week 3, 100% week 4. Monitor Postmaster Tools and seed-list placement daily at every step. A 4-week ramp on a 17-checks-passed stack reliably reaches steady-state without triggering filters. Faster ramps (under 2 weeks to 100%) trigger volume-spike filters even on perfect infrastructure.
Does Inboxlee handle the entire 17-item deliverability checklist automatically?
Inboxlee handles items 1-6 (DNS auth fully automated), item 7 (mailbox-per-domain ceiling enforced at checkout), item 8 (real-name mailbox provisioning), and surfaces items 14, 16, 17 in the dashboard for verification. You still handle items 9-13 (sending-tool configuration) and item 15 (suppression list) since those live in your sending tool. The 17-check becomes a 5-check on Inboxlee infrastructure.