email-deliverability

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:

1. What email sending platform is being used? (ESP or self-hosted)
2. Is this a shared IP or dedicated IP?
3. What is the current sending volume? (Daily/weekly/monthly)
4. What are current open rates and bounce rates?
5. Has there been a recent deliverability drop? (When did it start?)
6. Is the sending domain properly authenticated? (SPF, DKIM, DMARC)
7. How was the email list built? (Organic, purchased, scraped — critical question)
8. When was the last list cleaning?

Core Rules

1. Deliverability is earned, not bought. No tool or trick replaces genuine engagement signals.
2. Authentication is table stakes. SPF, DKIM, and DMARC must be configured correctly before anything else matters.
3. List quality is deliverability quality. A clean, engaged list delivers. A dirty list destroys sender reputation.
4. Never buy or rent email lists. This is the single fastest way to destroy deliverability.
5. Engagement drives placement. ISPs watch how recipients interact with your email. High engagement = inbox. Low engagement = spam.
6. Reputation is per domain AND per IP. Both matter, but domain reputation is increasingly dominant.
7. 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:

1. Identify all services that send email from your domain (ESP, transactional email, CRM, etc.)
2. Create a TXT record in your DNS:

   v=spf1 include:_spf.google.com include:sendgrid.net include:mailchimp.com ~all
   

3. Include ALL authorized senders
4. Use ~all (soft fail) or -all (hard fail — stricter)
5. 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:

1. Generate a DKIM key pair in your ESP (most ESPs do this automatically)
2. Add the public key as a TXT/CNAME record in your DNS
3. The record name is typically: selector._domainkey.yourdomain.com
4. 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:[e-mail]; ruf=mailto:[e-mail]; pct=100

Phase 2: Quarantine (after monitoring is clean)

v=DMARC1; p=quarantine; rua=mailto:[e-mail]; pct=25

Gradually increase pct from 25 to 50 to 100.

Phase 3: Reject (full protection)

v=DMARC1; p=reject; rua=mailto:[e-mail]; 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

1. Pristine traps — Addresses that were never real. Only appear on bought/scraped lists. Most damaging.
2. Recycled traps — Old addresses repurposed by ISPs. Result of never cleaning your list.
3. 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:

1. Identify: Segment subscribers who haven't engaged in 90+ days
2. Send Email 1: "We want to make sure you still want to hear from us. Click to stay subscribed."
3. Wait 7 days. If no action, send Email 2.
4. Send Email 2: "Last chance — click to keep getting our emails."
5. Wait 7 days. If no action, suppress from all future sends.
6. 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)

• SPF record configured and validated
• DKIM keys generated and DNS record added
• DMARC set to p=none for monitoring
• Domain registered 30+ days ago
• IP warming plan created
• List verified through an email validation service
• Double opt-in enabled for new subscribers
• Unsubscribe link present in all templates
• One-click unsubscribe header configured
• Google Postmaster Tools set up
• Blacklist monitoring configured

Ongoing (Monthly)

• Hard bounces removed
• Engagement segments updated
• Complaint rate reviewed (below 0.1%)
• Blacklist status checked
• Sending reputation monitored (Postmaster Tools)
• List growth sources audited (no purchased lists)

Quality Gate

Before sending any campaign, verify:

• Is the sending domain fully authenticated (SPF, DKIM, DMARC)?
• Is the list clean (no hard bounces, verified addresses)?
• Is the complaint rate below 0.1%?
• Is there a clear unsubscribe link and one-click unsubscribe header?
• Is the content free of spam trigger patterns?
• Is the text-to-image ratio balanced?
• Is the "From" name recognizable to recipients?
• Has the email been tested with a deliverability tool?
• Are inactive subscribers suppressed or segmented?
• Is the sending volume consistent with recent patterns (no sudden spikes)?