Emails Not Delivering: Diagnosis & Recovery for Zero Delivery Rate
Your emails are not being delivered (0% delivery rate)
Critical — total delivery failure requires immediate action.
Identify the failure point:
Check your ESP dashboard — what delivery status are emails showing?
Look for SMTP error codes (4xx = temporary, 5xx = permanent)
Is the issue for all recipients or specific domains?
Check if your sending account is suspended or rate-limited
What Could Be Causing This?
SMTP Authentication Failure (Invalid Credentials)
Most CommonIncorrect SMTP credentials, password change, or API key rotation prevents email sending.
How to confirm:
Check your ESP account settings — verify API credentials are correct. Check recent password changes.
Account Suspended or Rate-Limited
Most CommonDue to abuse, high bounce rate, or compliance issues, your account may be suspended or sending disabled.
How to confirm:
Check your ESP dashboard for account status. Look for warning messages or suspension notices.
SPF/DKIM/DMARC Rejection (Permanent)
CommonPermanent DMARC reject policy (p=reject) without proper SPF/DKIM alignment causes rejection.
How to confirm:
Check authentication checkers. Look for reject policies that are premature.
DNS Issue (SPF/DKIM Records Not Published)
CommonMissing or incorrectly published DNS records prevent authentication, causing rejection.
How to confirm:
Run SPF, DKIM, DMARC checkers. Verify DNS records are published and propagated.
Recipient Server Rejecting (Firewall/Filter)
Less CommonRecipient server may be blocking all mail from your IP or domain.
How to confirm:
Check if delivery failure is for specific domains (e.g., all @company.com fail). Test with different recipient.
Fix Playbook
Step 1: Verify SMTP Credentials & Account Status
- Log into your ESP account
- Check account status — is it active or suspended?
- Verify SMTP credentials (API key, username, password)
- If suspended, contact ESP support to reinstate
- If credentials changed, update your sending configuration
Step 2: Check Authentication (SPF, DKIM, DMARC)
- Run all three authentication checkers
- Look for "FAIL" or "SOFTFAIL" results
- Ensure DMARC policy is not set to p=reject prematurely
- Fix SPF/DKIM alignment if failing
- Test with a small send after fixes
Step 3: Verify DNS Configuration
- Check DNS propagation for SPF/DKIM/DMARC records
- Use DNS lookup tools to verify records are published
- If not published, publish them now
- Wait for propagation (5 min to 48 hours)
Step 4: Contact ESP Support if Account Suspended
- If account is suspended, contact ESP support immediately
- Ask about the reason for suspension
- Request reinstatement and provide corrective action plan
- This is urgent — most ESPs have 24-48 hour response
Prevention Checklist
- Monitor delivery rate daily
- Keep credentials secure — don't share SMTP/API keys
- Update credentials if you rotate passwords
- Maintain good authentication (SPF/DKIM/DMARC)
- Don't set DMARC to p=reject without full alignment
- Monitor account status and compliance alerts
Free Diagnostic Tools
Stop Fixing Deliverability Issues Reactively
The problem you just fixed probably cost you 20-30% of revenue while it was happening. InboxEagle would have detected it within 2 minutes and alerted you before placement dropped.
Real-time monitoring, AI diagnosis, and 24/7 alerts for every reputation change.
Start 14-Day Free Trial — No Card Needed