How to organize your email sending domains (basic guide)

📧 DOMAIN CHOICE FLOWCHART
┌─────────────────────────────┐
│   Your Brand: Example.com   │
├─────────────────────────────┤
│ ✅ Marketing emails:        │
│    offers.example.com       │
│                             │
│ ✅ Transactional emails:    │
│    info.example.com         │
│                             │
│ ❌ Cousin domains:          │
│    example-deals.com        │
└─────────────────────────────┘

Choosing the right domain for your email campaigns isn't just a technical decision—it's the foundation of your email deliverability. Get it wrong, and even your best content lands in spam. Get it right, and you build lasting trust with both recipients and email providers.

This guide breaks down the industry's best practices for choosing and setting up email domains, based on the M³AAWG guidelines that major email providers follow.

Quick Summary: The Golden Rule

Use subdomains of your main domain. Period.

If your company is example.com, send from:

news.example.com
offers.example.com
support.example.com

Never create "cousin domains" like example-deals.com or get-example-offers.com. They look like phishing attempts and hurt your deliverability.

Why Your Domain Choice Matters

Think of email domains like storefronts. Would you trust a Louis Vuitton store in a strip mall called "Luis Vutton Deals"? Neither do spam filters.

🏪 DOMAIN TRUST COMPARISON

Main Domain Family         vs.    Cousin Domains
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
✅ example.com                   ❌ example-deals.com
✅ offers.example.com            ❌ best-example-offers.com  
✅ news.example.com              ❌ example-newsletter.net

Trust Level: HIGH 📈             Trust Level: LOW 📉
Looks: LEGITIMATE               Looks: SUSPICIOUS
Result: INBOX                   Result: SPAM

The Problem with Cousin Domains

"Cousin domains" are separate domains that look related to your brand but aren't actually connected. They're tempting because they seem clever, but they're email deliverability poison.

Why People Use Them (And Why They Shouldn't)

❌ "We need a catchy campaign domain!"

summer-deals-at-example.com
shop-example-now.com
example-exclusive-offers.net

Why it fails: Recipients and spam filters can't verify these domains belong to you. They look exactly like phishing attempts. Often, too, people don't actually redirect the domains to their main domain, so they just go to a dead page.

✅ Do this instead:

summer.example.com
shop.example.com
offers.example.com

The Subdomain Strategy: Your Path to Success

Using subdomains keeps everything under your main domain umbrella while allowing perfect segmentation. Here's how to structure them:

Email Type → Subdomain Mapping

📮 SUBDOMAIN ARCHITECTURE

Your Main Domain: example.com
│
├─📰 Marketing Emails
│  └─ offers.example.com
│  └─ news.example.com
│  └─ updates.example.com
│
├─🛍️ Transactional Emails
│  └─ info.example.com
│  └─ orders.example.com
│  └─ account.example.com
│
├─🌍 Regional Emails
│  └─ uk.example.com
│  └─ eu.example.com
│  └─ asia.example.com
│
└─🏢 Department Emails
   └─ support.example.com
   └─ sales.example.com
   └─ hr.example.com

Why Subdomains Win

Instant Recognition: Recipients see "example.com" and know it's you
Reputation Inheritance: Benefits from your main domain's trust
Easy Management: All under one domain registration
Clear Segmentation: Different reputation tracking for each type
Professional Appearance: Looks legitimate to everyone

Setting Up Your Subdomain Strategy

Step 1: Map Your Email Streams

First, identify every type of email you send:

📊 EMAIL AUDIT WORKSHEET

□ Marketing campaigns (weekly newsletter, promotions)
□ Transactional emails (order confirmations, shipping)
□ Account emails (password resets, welcome emails)
□ Support emails (ticket updates, help responses)
□ Internal emails (employee communications)

Step 2: Assign Logical Subdomains

Match each email type to a clear, descriptive subdomain:

| Email Type | Good Subdomain | Bad Subdomain | |------------|----------------|---------------| | Newsletter | news.example.com | x7news.example.com | | Promotions | offers.example.com | DEALS.example.com | | Orders | orders.example.com | trans_01.example.com | | Support | help.example.com | noreply.example.com (though, Outlook don't like no reply addresses now) |

Pro tip: Keep subdomain names short, clear, and professional. No weird abbreviations or numbers.

Step 3: Maintain Consistency Across Headers

Your email headers should align like a perfectly organized closet:

📧 ALIGNED EMAIL HEADERS

Return-Path:    [email protected]
From:           [email protected]
DKIM Signature: d=news.example.com
Reply-To:       [email protected]

✅ All using news.example.com = ALIGNED

Or if using your main domain in the From:

📧 ORGANIZATIONALLY ALIGNED

Return-Path:    [email protected]
From:           [email protected]
DKIM Signature: d=example.com
Reply-To:       [email protected]

✅ All under example.com umbrella = ALIGNED

DNS Setup: Three Ways to Configure

Option 1: Direct Setup (Full Control)

Best when you manage your own DNS:

example.com DNS Records:
├─ news.example.com    TXT  "v=spf1 include:esp.com -all"
├─ news.example.com    MX   10 bounce.esp.com
├─ news.example.com    A    192.0.2.1
└─ selector._domainkey.news.example.com  TXT  "k=rsa; p=..."

Pros: Complete control, instant updates Cons: More technical knowledge required

Option 2: CNAME Delegation (Flexible)

Let your ESP manage some records (like is the case with Bento, we manage the DNS for you):

example.com DNS Records:
├─ news.example.com    CNAME  sending.your-esp.com
├─ link.news.example.com  CNAME  tracking.your-esp.com
└─ dkim._domainkey.news.example.com  CNAME  dkim.your-esp.com

Pros: ESP can update without your involvement Cons: Less visibility into changes

Option 3: NS Delegation (Hands-Off)

Delegate entire subdomain to ESP (rare that you'd do this, but some ESPs handle it this way):

example.com DNS Records:
└─ news.example.com    NS    ns1.your-esp.com
                       NS    ns2.your-esp.com

Pros: Zero maintenance required Cons: Complete loss of control

Volume Considerations: How Much Can Each Subdomain Handle?

📈 SUBDOMAIN VOLUME GUIDELINES

Low Volume (< 10K/month):
└─ Can use one subdomain for all emails

Medium Volume (10K-100K/month):
├─ Separate marketing from transactional
└─ Consider geographic separation

High Volume (100K+/month):
├─ Dedicated subdomain per email type
├─ Geographic subdomains (us.example.com)
├─ Department subdomains
└─ Consider multiple DKIM selectors

The Volume Balancing Act

Each subdomain needs enough volume to build reputation, but not so much it becomes a single point of failure:

⚖️ SUBDOMAIN VOLUME BALANCE

Too Few Emails                Too Many Emails
────────────────────────────────────────────
📉 No reputation built        📈 Reputation risk concentrated
🔄 Sporadic sending          🚫 One problem affects all
❓ Unpredictable delivery    💥 Harder to troubleshoot

Sweet spot: 10,000-500,000 emails/month per subdomain

Migration Strategy: Moving to Subdomain Structure

Already sending from your main domain or a cousin domain? Here's how to migrate safely:

Week 1-2: Foundation

📅 MIGRATION PHASE 1
1. Set up new subdomain infrastructure
2. Configure authentication (SPF, DKIM, DMARC)
3. Test with internal team emails
4. Send to small engaged segment (5%) or go live with a few automations that send low volume

Week 3-4: Transition

📅 MIGRATION PHASE 2
1. Move transactional emails first (higher engagement)
2. Gradually increase volume (5% → 25% → 50%)
3. Monitor metrics closely
4. Keep old domain as backup

Week 5+: Completion

📅 MIGRATION PHASE 3
1. Move remaining volume to subdomains
2. Set up forwarding from old addresses
3. Update all email templates and systems
4. Celebrate improved deliverability! 🎉

Common Subdomain Mistakes to Avoid

❌ The "Kitchen Sink" Subdomain

Mistake: Using mail.example.com for EVERYTHING Problem: No segmentation benefits, reputation risk Fix: Separate by email type

❌ The "Cryptic Code" Subdomain

Mistake: Using esp47.example.com or x3n.example.com Problem: Looks suspicious to recipients Fix: Use clear, descriptive names

❌ The "Set and Forget" Subdomain

Mistake: Never reviewing subdomain performance Problem: Issues go unnoticed until major problems Fix: Monthly subdomain health checks

Subdomain Security Best Practices

Protect your subdomains like you protect your main domain:

🔒 SECURITY CHECKLIST

□ Set up DMARC for each subdomain
□ Monitor for unauthorized use
□ Use strong DKIM keys (2048-bit)
□ Implement subdomain takeover protection
□ Regular security audits
□ Document all active subdomains

Quick Implementation Guide

Today (30 minutes):

Audit your current sending domains
List all email types you send
Map email types to proposed subdomains

This Week (2-3 hours):

Check subdomain availability
Plan DNS configuration approach
Coordinate with your ESP

Next Two Weeks:

Implement DNS changes
Test authentication thoroughly
Begin gradual migration

Tools for Success

Domain Planning:

Subdomain mapper: Plan your structure visually
DNS checker: Verify configurations
Authentication validators: Test SPF/DKIM/DMARC

Monitoring:

Postmaster tools: Track reputation by subdomain
DMARC reports: Monitor authentication success
Engagement metrics: Compare subdomain performance

The Psychology of Domain Trust

Recipients make split-second decisions about email legitimacy. Your domain choice influences that decision:

🧠 RECIPIENT THOUGHT PROCESS

Sees: offers.nike.com
Thinks: "That's really Nike" ✅

Sees: nike-super-deals.com  
Thinks: "Is this fake?" ❌

Sees: amaz0n.com
Thinks: "Definitely fake!" 🚨

Scaling Your Subdomain Strategy

As your email program grows, your subdomain strategy should evolve:

Startup Phase (0-50K subscribers):

1-2 subdomains maximum
Focus on authentication basics

Growth Phase (50K-500K subscribers):

3-5 subdomains by email type
Consider geographic separation

Enterprise Phase (500K+ subscribers):

Full subdomain architecture
Department and regional subdomains
Multiple DKIM selectors
Dedicated IP considerations

The Bottom Line

Your sending domain is your email program's foundation. Cousin domains are like building on quicksand—they might seem stable at first, but they'll eventually sink your deliverability.

By using subdomains of your main domain, you're building on bedrock. It's the strategy that ISPs expect, recipients trust, and successful email programs are built on.

Remember: Every major brand uses subdomains for a reason. They work.

Need help planning your subdomain strategy? Start with these three subdomains: news.yourdomain.com for marketing, account.yourdomain.com for transactional, and support.yourdomain.com for customer service. You can always expand or switch to a different subdomain later.