Email Deliverability Best Practices: Get Your Emails to the Inbox

You can craft the perfect email, but it means nothing if it lands in spam. Email deliverability—getting your emails into the inbox—is the foundation of successful email marketing. Here's everything you need to know.

What is Email Deliverability?

Deliverability measures whether your emails reach the inbox vs. spam folder (or get blocked entirely). Key metrics:

• Delivery rate: % of emails that don't bounce
• Inbox placement rate: % that reach the inbox (not spam)
• Spam complaint rate: % of recipients who mark as spam

The Big Three: Email Authentication

1. SPF (Sender Policy Framework)

SPF tells email servers which IPs are authorized to send from your domain.

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

Add this as a TXT record on your domain. Without SPF, your emails are more likely to be marked as spam.

2. DKIM (DomainKeys Identified Mail)

DKIM adds a cryptographic signature to verify emails weren't modified in transit.

v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQ...

Your email service provider generates the DKIM key—you add it as a TXT record on your domain.

3. DMARC (Domain-based Message Authentication)

DMARC tells receivers what to do if SPF/DKIM fail, and sends you reports.

v=DMARC1; p=quarantine; rua=mailto:dmarc@example.com; pct=100

Start with p=none (monitoring only), then move to p=quarantine or p=reject.

List Hygiene Best Practices

Regular List Cleaning

• Remove hard bounces immediately - Invalid addresses hurt your reputation
• Remove inactive subscribers after 6-12 months of no engagement
• Use double opt-in to confirm valid email addresses
• Process unsubscribes promptly (legally required within 10 days)

Warning Signs

• Bounce rate above 2%
• Spam complaint rate above 0.1%
• Open rates declining over time
• High unsubscribe rates (above 0.5%)

Content Best Practices

Avoid Spam Trigger Words

Spam filters look for patterns. Avoid these in subject lines:

• FREE!!! (especially with excessive punctuation)
• ACT NOW
• LIMITED TIME
• GUARANTEED
• Click here
• $$$ or money-related terms

Maintain Good Text-to-Image Ratio

• Aim for 60% text, 40% images (or higher text ratio)
• Never send image-only emails
• Always include alt text for images

HTML Quality Matters

Mailglass Lite validates HTML that can trigger spam filters:

• Broken HTML tags
• Missing alt text
• Excessive links
• Hidden text (white text on white background)
• Suspicious redirects

Technical Best Practices

Sending Infrastructure

• Use a reputable ESP (Mailchimp, SendGrid, etc.) - They maintain good IP reputation
• Warm up new IPs gradually - Start with small volumes
• Monitor blacklists - Check mxtoolbox.com regularly
• Separate transactional and marketing - Use different IPs/domains

Essential Headers

From: newsletter@yourdomain.com
Reply-To: support@yourdomain.com
List-Unsubscribe: <mailto:unsub@domain.com>, <https://domain.com/unsub>
List-Unsubscribe-Post: List-Unsubscribe=One-Click

Required Elements

• Physical mailing address (CAN-SPAM requirement)
• Clear unsubscribe link
• Accurate "From" name and address

Engagement Signals

Mailbox providers watch how recipients interact with your emails:

Positive Signals

• Opening emails
• Clicking links
• Replying to emails
• Moving from spam to inbox
• Adding sender to contacts

Negative Signals

• Marking as spam
• Deleting without opening
• Never opening emails
• Moving to spam folder

Sender Reputation Factors

Factor	Impact	Target
Bounce rate	High	Below 2%
Spam complaints	Very High	Below 0.1%
Spam trap hits	Very High	Zero
Blacklist listings	Critical	None
Authentication	High	SPF/DKIM/DMARC pass
Engagement	Medium	Above industry average

Monitoring Tools

• Google Postmaster Tools - Free domain reputation data for Gmail
• Microsoft SNDS - Smart Network Data Services for Outlook
• MxToolbox - Blacklist monitoring and DNS checks
• Mail-tester.com - Score your emails for deliverability

Deliverability Checklist

Authentication

• ☐ SPF record configured
• ☐ DKIM signing enabled
• ☐ DMARC policy set
• ☐ "From" domain matches authentication

Content

• ☐ Subject line avoids spam triggers
• ☐ Good text-to-image ratio (60/40)
• ☐ All images have alt text
• ☐ Physical address included
• ☐ Unsubscribe link visible

List Health

• ☐ Hard bounces removed
• ☐ Inactive subscribers cleaned
• ☐ Double opt-in used
• ☐ Unsubscribes processed

Technical

• ☐ HTML is clean and valid
• ☐ List-Unsubscribe header present
• ☐ Not on any blacklists
• ☐ Sending from warmed IP

If You're in Spam

Already landing in spam? Here's how to recover:

1. Check authentication - Verify SPF/DKIM/DMARC
2. Review content - Use Mailglass Lite to check for issues
3. Clean your list - Remove bounces and inactive subscribers
4. Check blacklists - Request removal if listed
5. Reduce volume - Send to engaged users only
6. Encourage engagement - Ask users to add you to contacts
7. Be patient - Reputation rebuilds over weeks/months

Key Takeaways

• Set up SPF, DKIM, and DMARC authentication
• Maintain list hygiene—remove bounces and inactive users
• Avoid spam trigger words and bad HTML
• Monitor your sender reputation regularly
• Focus on engagement to build positive reputation

Want to check your email for deliverability issues? Mailglass Lite validates HTML quality and flags content that might trigger spam filters.