Email Deliverability: Making Sure Your Emails Reach the Inbox
You've crafted the perfect email, but it means nothing if it lands in spam. Email deliverability is the art and science of getting your emails into recipients' inboxes. Let's explore what affects deliverability and how to improve it.
What is Email Deliverability?
Deliverability is the measure of how successfully your emails reach recipients' inboxes (not spam folders). It rests on four main factors, each covered in this guide:
Authentication
Proving you're who you say you are with SPF, DKIM and DMARC.
Reputation
Your sending history and trustworthiness, tracked per IP and domain.
List hygiene
Sending only to real, engaged subscribers who asked to hear from you.
Content
What you say and how you say it — avoiding spam triggers and noise.
Authentication: The Foundation
Email authentication is the technical foundation of deliverability. Without it, mailbox providers have no way to trust your emails are legitimate.
- SPF and DKIM authenticating, with at least one aligned to the From: domain
- A published DMARC policy (
p=noneis the minimum) - One-click List-Unsubscribe header (RFC 8058) for marketing mail
- Sustained spam-complaint rate below 0.3% (target < 0.1%)
- TLS for the SMTP connection
Authentication Checklist
- SPF: Publish a record listing all your sending IPs and services
- DKIM: Sign all outgoing emails with your domain's private key
- DMARC: Set policy to at least
p=quarantine, ideallyp=reject - Alignment: Ensure your "From" domain matches SPF/DKIM domains
Reputation: Your Email Credit Score
Your sending reputation is like a credit score for email. Mailbox providers track your sending behavior and use it to decide whether to trust future emails.
Factors Affecting Reputation
| Factor | Good | Bad |
|---|---|---|
| Bounce Rate | < 2% | > 5% |
| Spam Complaints | < 0.1% | > 0.3% |
| Spam Trap Hits | 0 | Any |
| Engagement Rate | > 20% opens | < 5% opens |
Types of Reputation
- IP Reputation: Based on the sending server's IP address. Shared IPs carry shared risk.
- Domain Reputation: Based on your domain's sending history. Follows your domain everywhere.
- User Reputation: Some providers track reputation at the individual email address level.
List Hygiene: Quality Over Quantity
A clean email list is essential for good deliverability. Sending to bad addresses damages your reputation fast.
List Hygiene Best Practices
- Use double opt-in — require subscribers to confirm their email address.
- Remove hard bounces immediately and clean subscribers inactive for 6–12 months.
- Make unsubscribing easy — a visible link prevents spam complaints.
- Retry hard bounces — they signal an invalid address and hurt reputation.
- Buy lists — purchased lists are full of spam traps and unengaged contacts.
- Hide the unsubscribe link — frustrated recipients hit "spam" instead.
Understanding Spam Traps
Spam traps are email addresses used to identify senders with poor list practices:
- Pristine traps: Addresses that never signed up for anything - hitting these is very bad
- Recycled traps: Old addresses repurposed as traps - indicates you have stale lists
- Typo traps: Common misspellings (gmal.com, yahooo.com) - indicates no validation
Content: What You Say Matters
Even with perfect authentication and reputation, poor content can land you in spam.
Content Red Flags
- ALL CAPS subjects or excessive punctuation!!!
- Spam trigger words (FREE, ACT NOW, LIMITED TIME)
- Image-only emails with no text
- Mismatched display text and URLs
- URL shorteners (bit.ly, tinyurl)
- Too many links or images
Content Best Practices
- Maintain a healthy text-to-image ratio (60% text, 40% images)
- Use your actual domain for links, not redirects
- Include a plain text version alongside HTML
- Keep subject lines under 50 characters
- Always include your physical mailing address (required by law)
Technical Setup for Deliverability
DNS Records
- Reverse DNS (PTR): Your sending IP should have a PTR record pointing to your domain
- MX Records: Even if you only send, having MX records looks more legitimate
- HELO/EHLO: Configure your mail server's identity to match your domain
Sending Infrastructure
- Dedicated IPs: For high-volume senders, use dedicated IPs you control
- IP Warming: Gradually increase volume on new IPs
- Segmentation: Separate transactional from marketing email infrastructure
Monitoring Your Deliverability
You can't improve what you don't measure. Set up these monitoring systems:
Key Metrics to Track
- Inbox Placement Rate: Percentage of emails reaching inbox vs spam
- Bounce Rate: Hard bounces (invalid) and soft bounces (temporary)
- Spam Complaint Rate: People marking your email as spam
- Engagement Metrics: Open rates, click rates, reply rates
Feedback Loops
Sign up for Feedback Loops (FBLs) with major providers to receive notifications when users mark your email as spam:
- Microsoft SNDS and JMRP
- Google Postmaster Tools
- Yahoo Complaint Feedback Loop
rua=) to receive daily
summaries of who's sending email as your domain and whether it's passing authentication.
Deliverability Troubleshooting
If You're Landing in Spam
Work through these steps in order to recover inbox placement:
Verify authentication
Confirm SPF, DKIM and DMARC are properly configured and aligned.
Check blacklists
Make sure your IP and domain aren't listed on any blocklists.
Audit your content
Review recent campaigns for spam triggers and broken links.
Inspect your rates
Check bounce and complaint rates for anything trending the wrong way.
Throttle volume
Reduce sending volume temporarily to ease provider throttling.
Re-engage gradually
Focus on your most engaged subscribers first to rebuild reputation.
Common Issues and Fixes
| Problem | Likely Cause | Solution |
|---|---|---|
| Gmail spam folder | Low engagement, authentication issues | Check Postmaster Tools, improve content |
| Bouncing everywhere | IP blacklisted | Check MXToolbox, request delisting |
| Slow delivery | Throttling due to reputation | Reduce volume, warm up slowly |
| DMARC failures | Third-party sender not configured | Add to SPF, configure DKIM |
Test Your Email Setup
Check your domain's email security configuration and get recommendations for improvement: