| name | email-deliverability |
| description | Optimize email deliverability through authentication, list hygiene, and sender reputation management. Use when improving inbox placement rates. |
| origin | ECM |
Email Deliverability
When to Activate
Use this skill when:
- Setting up email infrastructure for a new domain or sender
- Diagnosing deliverability problems (emails going to spam)
- Warming a new IP or domain
- Cleaning an email list
- Setting up SPF, DKIM, and DMARC
- Improving inbox placement rates
- Planning a re-permission or re-engagement campaign
First Questions
Before optimizing deliverability, clarify:
- What email sending platform is being used? (ESP or self-hosted)
- Is this a shared IP or dedicated IP?
- What is the current sending volume? (Daily/weekly/monthly)
- What are current open rates and bounce rates?
- Has there been a recent deliverability drop? (When did it start?)
- Is the sending domain properly authenticated? (SPF, DKIM, DMARC)
- How was the email list built? (Organic, purchased, scraped — critical question)
- When was the last list cleaning?
Core Rules
- Deliverability is earned, not bought. No tool or trick replaces genuine engagement signals.
- Authentication is table stakes. SPF, DKIM, and DMARC must be configured correctly before anything else matters.
- List quality is deliverability quality. A clean, engaged list delivers. A dirty list destroys sender reputation.
- Never buy or rent email lists. This is the single fastest way to destroy deliverability.
- Engagement drives placement. ISPs watch how recipients interact with your email. High engagement = inbox. Low engagement = spam.
- Reputation is per domain AND per IP. Both matter, but domain reputation is increasingly dominant.
- Monitor proactively. Don't wait for problems — monitor deliverability metrics weekly.
Email Authentication Setup
SPF (Sender Policy Framework)
SPF tells receiving mail servers which IPs are authorized to send email on behalf of your domain.
Setup:
- Identify all services that send email from your domain (ESP, transactional email, CRM, etc.)
- Create a TXT record in your DNS:
v=spf1 include:_spf.google.com include:sendgrid.net include:mailchimp.com ~all
- Include ALL authorized senders
- Use
~all (soft fail) or -all (hard fail — stricter)
- Maximum 10 DNS lookups — consolidate if needed
Common mistakes:
- Multiple SPF records (you can only have ONE per domain)
- Exceeding the 10 DNS lookup limit
- Forgetting to include all sending services
DKIM (DomainKeys Identified Mail)
DKIM adds a digital signature to your emails, proving they haven't been tampered with in transit.
Setup:
- Generate a DKIM key pair in your ESP (most ESPs do this automatically)
- Add the public key as a TXT/CNAME record in your DNS
- The record name is typically:
selector._domainkey.yourdomain.com
- Test with a DKIM validator tool
Best practices:
- Use 2048-bit keys (minimum)
- Rotate keys annually
- Use a unique selector per sending service
DMARC (Domain-based Message Authentication, Reporting & Conformance)
DMARC tells receiving servers what to do with emails that fail SPF and DKIM checks.
Setup (progressive):
Phase 1: Monitor (first 2-4 weeks)
v=DMARC1; p=none; rua=mailto:dmarc-reports@yourdomain.com; ruf=mailto:dmarc-forensic@yourdomain.com; pct=100
Phase 2: Quarantine (after monitoring is clean)
v=DMARC1; p=quarantine; rua=mailto:dmarc-reports@yourdomain.com; pct=25
Gradually increase pct from 25 to 50 to 100.
Phase 3: Reject (full protection)
v=DMARC1; p=reject; rua=mailto:dmarc-reports@yourdomain.com; pct=100
Never skip Phase 1. Jumping to p=reject without monitoring can block legitimate emails.
BIMI (Brand Indicators for Message Identification)
BIMI displays your brand logo next to emails in supported inboxes (Gmail, Yahoo, Apple Mail).
Requirements:
- DMARC policy must be
p=quarantine or p=reject
- A verified brand logo in SVG format
- A Verified Mark Certificate (VMC) from a certificate authority (for Gmail)
- DNS record:
default._bimi.yourdomain.com with logo URL
IP Warming Schedule
New dedicated IPs must be warmed gradually. Sending too much too fast flags spam filters.
Warming Plan (Typical)
| Day | Emails per Day | Notes |
|---|
| 1-2 | 50-100 | Send to your most engaged subscribers only |
| 3-4 | 200-500 | Continue with engaged subscribers |
| 5-7 | 500-1,000 | Begin expanding to broader engaged segments |
| 8-14 | 1,000-5,000 | Monitor bounces and complaints closely |
| 15-21 | 5,000-15,000 | Gradually include less-engaged segments |
| 22-30 | 15,000-50,000 | Approaching full volume |
| 31+ | Full volume | Maintain consistent sending patterns |
Warming rules:
- Start with your MOST engaged subscribers (high open rates)
- Never skip days during warming — consistency matters
- If bounce rate exceeds 5% or complaint rate exceeds 0.1%, pause and investigate
- Send real, valuable emails during warming (not test emails)
- Maintain consistent daily volume — don't spike
Domain Warming
New domains also need warming, even on shared IPs:
- Register the domain at least 30 days before first send
- Set up a basic website on the domain
- Configure all authentication (SPF, DKIM, DMARC)
- Start with transactional emails before marketing emails
- Follow the same gradual volume increase as IP warming
List Hygiene Protocols
Regular Cleaning Schedule
- Monthly: Remove hard bounces (automatic in most ESPs)
- Quarterly: Suppress subscribers with zero engagement in 90 days
- Biannually: Run email verification/validation on full list
- Annually: Re-permission campaign for inactive subscribers
Email Verification
Before sending to old or imported lists, verify addresses using a service (ZeroBounce, NeverBounce, BriteVerify):
- Remove invalid addresses
- Remove role-based addresses (info@, admin@, support@)
- Remove disposable email addresses
- Flag catch-all domains for monitoring
Engagement-Based List Segments
| Segment | Definition | Action |
|---|
| Highly engaged | Opened or clicked in last 30 days | Send freely |
| Engaged | Opened or clicked in last 90 days | Send normally |
| At risk | No open in 60-90 days | Reduce frequency, re-engage |
| Dormant | No open in 90-180 days | Re-engagement sequence only |
| Dead | No open in 180+ days | Suppress or sunset |
Bounce Management
Hard Bounces
- Invalid addresses — remove immediately and permanently
- Never re-send to a hard-bounced address
- If hard bounce rate exceeds 2% on any send, stop and investigate
Soft Bounces
- Temporary issues (full mailbox, server down)
- Retry 2-3 times over 48-72 hours
- If an address soft-bounces 3+ times consecutively, treat as hard bounce
Spam Trap Avoidance
Types of Spam Traps
- Pristine traps — Addresses that were never real. Only appear on bought/scraped lists. Most damaging.
- Recycled traps — Old addresses repurposed by ISPs. Result of never cleaning your list.
- Typo traps — Common typo domains (gmial.com, yahooo.com). Result of no email validation on forms.
Prevention
- Never buy or scrape email lists (prevents pristine traps)
- Clean inactive subscribers regularly (prevents recycled traps)
- Use email validation on signup forms (prevents typo traps)
- Use double opt-in for new subscribers
- Monitor blacklist status regularly (MXToolbox, Spamhaus)
Re-Permission Campaign
When deliverability is damaged or a list has been neglected, run a re-permission campaign:
- Identify: Segment subscribers who haven't engaged in 90+ days
- Send Email 1: "We want to make sure you still want to hear from us. Click to stay subscribed."
- Wait 7 days. If no action, send Email 2.
- Send Email 2: "Last chance — click to keep getting our emails."
- Wait 7 days. If no action, suppress from all future sends.
- Result: A smaller but healthier, higher-engagement list.
Important: You will lose subscribers. This is intentional. A smaller, engaged list outperforms a large, disengaged one every time.
Deliverability Monitoring
Metrics to Track Weekly
| Metric | Healthy Range | Red Flag |
|---|
| Open rate | 20-40% | Below 15% |
| Bounce rate | Below 2% | Above 3% |
| Complaint rate | Below 0.05% | Above 0.1% |
| Unsubscribe rate | Below 0.3% | Above 0.5% |
| Spam placement rate | Below 5% | Above 10% |
| Inbox placement rate | Above 90% | Below 80% |
Monitoring Tools
- Google Postmaster Tools — Free. Shows domain reputation with Gmail.
- Microsoft SNDS — Free. Shows reputation with Outlook/Hotmail.
- MXToolbox — Blacklist monitoring, DNS checks.
- GlockApps / Mail-Tester — Inbox placement testing across ISPs.
- Your ESP's dashboard — Bounce, complaint, and engagement data.
Content Factors Affecting Deliverability
What Triggers Spam Filters
- ALL CAPS in subject lines
- Excessive exclamation marks!!!
- Spam trigger words in subject lines (free, act now, limited time, congratulations)
- Image-only emails with no text
- Mismatched "From" name and domain
- Missing unsubscribe link
- Misleading subject lines
- Shortened URLs (bit.ly, etc.) — use full branded URLs
- Too many links relative to text
What Helps Deliverability
- Plain text version included alongside HTML
- Balanced text-to-image ratio (60:40 text-to-image minimum)
- Clear, recognizable "From" name
- Consistent sending frequency
- One-click unsubscribe header (now required by Gmail and Yahoo)
- Relevant, expected content that matches subscriber expectations
Deliverability Checklist
Before First Send (New Domain/IP)
Ongoing (Monthly)
Quality Gate
Before sending any campaign, verify:
