Email Deliverability Issues: Common Problems and How to Fix Them

Troubleshooting

Email deliverability issues are frustrating because they often happen silently. Your emails leave your outbox, but they never reach recipients — or they land in spam without anyone telling you. This guide covers the most common deliverability problems and how to diagnose and fix them.

Authentication Issues

Authentication problems are the most common and most fixable deliverability issues.

SPF Failures

Symptoms:

• Emails rejected with SPF failure messages
• Emails landing in spam at providers that check SPF strictly
• "Not authorized" errors in bounce messages

Common causes:

• SPF record doesn't include your sending service
• Too many DNS lookups (exceeds 10-lookup limit)
• Syntax errors in SPF record
• Missing SPF record entirely

How to fix:

1. Check your SPF record for validity
2. Ensure all sending services are included
3. Flatten if exceeding lookup limit
4. Fix any syntax errors

DKIM Failures

Symptoms:

• DKIM verification fails in email headers
• Reduced deliverability despite valid SPF
• "DKIM signature invalid" in authentication results

Common causes:

• DNS record doesn't match signing configuration
• Wrong selector being used
• Key rotation without updating DNS
• DKIM not enabled on sending service

How to fix:

1. Test your DKIM configuration
2. Verify DNS records match your email provider's requirements
3. Check that signing is enabled
4. Confirm correct selector is being used

DMARC Failures

Symptoms:

• Emails failing DMARC despite SPF or DKIM passing
• "DMARC fail" in authentication headers
• Emails rejected by providers with strict DMARC enforcement

Common causes:

• Alignment failure (From domain doesn't match authentication domains)
• No DMARC record published
• Policy set to reject without proper testing

How to fix:

1. Review your DMARC configuration
2. Ensure SPF and/or DKIM domains align with From address
3. Start with p=none policy for monitoring
4. Review DMARC reports to identify failures

Reputation Issues

Reputation problems take longer to fix than authentication issues.

Blacklisting

Symptoms:

• Sudden delivery failures to specific providers
• Bounce messages mentioning blacklists
• Overall delivery rate drops

How to diagnose:

1. Check blacklist status
2. Review recent sending for problems that triggered listing
3. Check for compromised accounts or systems

How to fix:

1. Identify the cause (high complaints, spam trap hits, etc.)
2. Fix the underlying problem
3. Request removal following each blacklist's process
4. Monitor to prevent relisting

Low Sender Score

Symptoms:

• Gradual decline in deliverability
• Increased spam folder placement
• Provider tools showing poor reputation

Common causes:

• High complaint rates over time
• High bounce rates indicating poor list quality
• Low engagement from recipients
• Spam trap hits

How to fix:

1. Clean your email list thoroughly
2. Improve targeting to increase engagement
3. Make unsubscribing easier (reduces complaints)
4. Send to engaged recipients first to rebuild
5. Wait — reputation recovers slowly

Provider-Specific Reputation

Symptoms:

• Good deliverability everywhere except one provider
• Sudden filtering at Gmail, Outlook, or Yahoo specifically
• Provider-specific bounce messages

How to diagnose:

• Use Google Postmaster Tools for Gmail
• Register with Microsoft SNDS for Outlook
• Check provider-specific feedback loops

How to fix:

1. Address issues specific to that provider
2. Focus on engagement from those recipients
3. Review their specific requirements
4. May need to reduce volume temporarily

List Quality Issues

Poor list quality causes recurring deliverability problems.

High Bounce Rates

Symptoms:

• Bounce rate above 2%
• Many hard bounces on sends
• Increasing bounces over time

Common causes:

• Old list with decayed addresses
• Purchased or scraped list
• Data entry errors at collection
• List not maintained over time

How to fix:

1. Remove all hard-bounced addresses immediately
2. Validate list before sending
3. Implement confirmed opt-in for new subscribers
4. Regularly clean unengaged subscribers

Spam Trap Hits

Symptoms:

• Blacklist listings mentioning spam traps
• Sudden reputation drops
• Delivery failures without clear cause

Common causes:

• Purchased lists containing traps
• Old lists with recycled trap addresses
• Scraping addresses from websites
• Not removing inactive subscribers

How to fix:

1. Use trap-detection services to identify potential traps
2. Remove all addresses that haven't engaged in 6+ months
3. Never use purchased or scraped lists
4. Implement strict list hygiene practices

High Complaint Rates

Symptoms:

• Complaint rate above 0.1%
• Reputation drops in provider tools
• Feedback loop reports showing complaints

Common causes:

• Emailing people who didn't opt in
• Sending too frequently
• Content not matching subscriber expectations
• Difficult unsubscribe process

How to fix:

1. Review how addresses were collected
2. Make unsubscribe links prominent and working
3. Reduce frequency or let subscribers choose
4. Improve content relevance
5. Send re-permission campaigns to uncertain subscribers

Infrastructure Issues

Technical problems with your sending infrastructure.

Sending IP Problems

Symptoms:

• Deliverability issues specific to your sending IP
• Rejections mentioning IP reputation
• Better delivery from different infrastructure

How to diagnose:

1. Check IP blacklist status
2. Review IP reputation in provider tools
3. Compare delivery from different IPs

How to fix:

1. Address what caused IP reputation damage
2. Request blacklist removal if listed
3. Consider switching IPs (requires warmup)
4. Move to dedicated IP for isolation

DNS Configuration Errors

Symptoms:

• Intermittent authentication failures
• DNS-related bounce messages
• Records showing correctly sometimes but not always

Common causes:

• DNS propagation issues
• TTL settings causing caching problems
• Conflicting records
• Zone file errors

How to fix:

1. Verify all DNS records are correct
2. Allow time for propagation after changes
3. Check for conflicting records
4. Test from multiple locations

Email Server Misconfiguration

Symptoms:

• Delivery failures regardless of recipient provider
• Technical errors in bounce messages
• Authentication working but delivery failing

Common causes:

• Incorrect SMTP configuration
• Missing or wrong reverse DNS
• TLS/SSL issues
• Server not properly identifying itself

How to fix:

1. Review server configuration
2. Ensure reverse DNS is configured correctly
3. Verify TLS is working
4. Check server HELO/EHLO identification

Content Issues

Content rarely causes deliverability problems on its own but can contribute.

Spam-Like Content

Symptoms:

• Emails filtered despite good authentication and reputation
• Content-related flags in spam filter results
• Specific emails fail while others succeed

What to check:

• Subject line patterns (caps, excessive punctuation)
• Body content (spam trigger words, suspicious formatting)
• Link destinations (URL shorteners, suspicious domains)
• Image-to-text ratio

How to fix:

1. Review content against spam filter best practices
2. Test content changes to see impact
3. Use plain text or simpler HTML
4. Reduce or remove suspicious links

Missing Required Elements

Symptoms:

• Filtering at providers that check for compliance
• Violations of CAN-SPAM or other regulations

Required elements:

• Physical mailing address
• Unsubscribe link
• Accurate sender identification
• Honest subject lines

How to fix: Ensure every email includes all required elements.

Troubleshooting Process

When facing deliverability issues, follow this diagnostic order:

Step 1: Check Authentication

Verify SPF, DKIM, and DMARC. Fix any failures before investigating further.

Step 2: Check Blacklists

Run a blacklist check. If listed, address the cause and request removal.

Step 3: Review Metrics

Check bounce rates, complaint rates, and engagement. Identify any metrics that are out of normal range.

Step 4: Test Delivery

Send test emails to accounts at major providers. Check where they land and review headers.

Step 5: Check Provider Tools

Review Google Postmaster Tools, Microsoft SNDS, and any ESP-provided deliverability data.

Step 6: Investigate Recent Changes

Consider what changed recently — new email service, DNS changes, list changes, content changes.

Stop Worrying About Email Deliverability

The Email Deliverability Suite monitors your SPF, DKIM, DMARC, MX records and blacklist status daily. Get alerts when something breaks — before your emails stop arriving.