Email Deliverability Checklist: Protect & Scale Sending Health
Key Metrics & Outcomes
Data-driven insights that demonstrate the strategic value and measurable impact of implementing these approaches
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1. Authentication
Email authentication is non-negotiable in 2025. Major providers require proper authentication and will reject or deprioritize unauthenticated mail.
SPF: Add TXT records to DNS listing all IPs authorized to send from your domain. Include your ESP, marketing tools, and any other sending services.
DKIM: Generate public/private key pairs and publish the public key in DNS. Your sending service signs each message with the private key for verification. Use 2048-bit keys for security.
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DMARC: Policy tells receivers what to do with failed checks. Start with 'p=none' to monitor, progress to 'p=quarantine' then 'p=reject'. Enable reporting to catch issues.
Custom tracking domains are critical. Use branded subdomains (track.yourdomain.com) instead of generic URLs to maintain domain alignment and build trust.
2. Progressive Warmup
New domains and addresses have zero reputation. High volumes immediately trigger spam filters and can permanently damage deliverability.
Follow progressive warmup over 2-4 weeks: • Week 1: 10-20 sends/day • Week 2: 40-80 sends/day • Week 3: 100-150 sends/day • Week 4+: 200-300 sends/day (gradually increase)
Send to high-engagement targets likely to open and reply. Mix in seed accounts (internal addresses, partners) you can manually engage with for positive signals.
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Vary sending patterns—stagger throughout the day instead of all at 9 AM. Mix message length and content structure to appear human. Monitor engagement obsessively; if opens drop below 30% or spam complaints appear, pause and investigate.
Sample distribution – replace with live metrics
3. Content Hygiene
Modern spam filters use sophisticated NLP models. Obvious triggers have evolved beyond 'FREE MONEY!!!' to subtler patterns.
Avoid: excessive capitalization, too many exclamation points/emojis, deceptive subject lines, heavy image-to-text ratios (aim 60%+ text), multiple links in short emails (max 2-3), shortened URLs, attachments in cold emails, trigger words (free, guarantee, act now).
What works: Personalization in first 2-3 sentences signals human-written content. Reference specific details about the prospect's company, role, or recent activity.
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Use proper paragraphs with line breaks. Include professional signature with contact info. Add unsubscribe link (required by CAN-SPAM and GDPR). A/B test everything—what triggers filters varies by industry and audience.
4. Continuous Monitoring
Deliverability isn't set-and-forget. Reputation decays without maintenance, and problems compound quickly if undetected.
Track weekly: Bounce rate (hard bounces <2%, soft bounces resolve in 24-48hr), spam complaint rate (<0.1%, even 1 per 100 sends risks blocklisting), inbox placement (seed testing across 20+ providers), sender reputation (Google Postmaster, Microsoft SNDS, Sender Score 0-100, Barracuda blocklist checking).
Engagement metrics matter—ISPs track opens, clicks, replies, and time spent reading. Low engagement (<20% opens) signals recipients don't value emails, even without spam marks.
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Set up alerts for threshold breaches. If bounce rate exceeds 3% or spam complaints spike, pause campaigns immediately and diagnose before continuing.
Sample distribution – replace with live metrics
5. Remediation Actions
When deliverability declines, quick action prevents permanent damage.
Bounce rate spike (>5%): Pause mailboxes, review list sources for stale data/spam traps, re-verify addresses, check for typos (gmial.com), remove hard bounces permanently.
Spam complaints increase (>0.2%): Review content for triggers, ensure unsubscribe links work, check targeting relevance, reduce send velocity 50%, improve personalization.
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Inbox placement drops (<85%): Verify SPF/DKIM/DMARC alignment, check tracking domain configuration, review content, tighten targeting, pause low-engagement segments, re-warm with high-quality sends.
Reputation declines: Rotate to fresh mailboxes/IPs while repairing, request delisting from blocklists (include remediation plan), reduce volume to rebuild gradually, focus on highest-quality segments only.
Document all issues and fixes—deliverability problems often stem from systematic issues that recur without process changes.