The 550 5.7.0 error means the recipient’s server rejected your email based on local security policy — typically failed SPF/DKIM/DMARC authentication or relay restrictions.
Fix it by validating your DNS authentication records, ensuring all sending IPs are authorized, and verifying your mail routing configuration.
The 5.7.0 code is intentionally generic — “other or undefined security status.” Providers use it when rejecting mail for policy reasons without specifying exactly which policy triggered.
This vagueness makes diagnosis harder, but the causes typically cluster around authentication failures and relay misconfigurations.
Quick skim — 550 5.7.0 error overview
The 550 5.7.0 error indicates security or policy-based rejection without specific cause identification.
| Attribute | Details |
| Error code | 550 5.7.0 |
| Category | Security/policy violation |
| Meaning | Message rejected due to policy (unspecified) |
| Severity | Permanent (hard bounce) |
| Common causes | SPF/DKIM/DMARC failure, relay denied, content policy |
| Fix approach | Fix authentication → verify relay → check content |
What does 550 5.7.0 mean?
The enhanced code 5.7.0 means “other or undefined security status” — the receiving server rejected the message for security/policy reasons, but didn’t specify which rule triggered. Providers use this when:
- Multiple authentication checks failed
- Local policy blocked the message without detailed categorization
- Relay configuration prevented delivery
Provider variations
The message and cause could be different for providers:
| Provider | Common Message | Likely Cause |
| Gmail SMTP Relay | 550 5.7.0 Email relay denied | Relay not configured for sender |
| Exchange Online | 550 5.7.0 Message rejected per DMARC policy | DMARC alignment failure |
| Generic | 550 5.7.0 Local policy violation | SPF fails, content filter, or other |
Vs specific 5.7.x codes
When providers have specific information, they use more precise codes:
| Code | Specific Meaning |
| 5.7.0 | Generic security rejection |
| 5.7.1 | Delivery not authorized (spam/reputation) |
| 5.7.23 | SPF validation failed |
| 5.7.25 | Reverse DNS (PTR) validation failed |
| 5.7.26 | Multiple authentication failures |
The 5.7.0 code appears when the server’s response falls outside these specific categories.
Why does the 550 5.7.0 error occur?
Most 5.7.0 rejections trace back to authentication or relay problems — security measures rejecting unauthenticated or misconfigured senders.
SPF failure
The receiving server checked your SPF record and determined that the sending IP isn’t authorized. Common causes:
- SPF syntax errors
- Sending IP not included in SPF
- SPF exceeds 10 DNS lookups (permerror)
- Third-party tools (CRM, marketing platforms) not authorized
DKIM failure
DKIM signatures didn’t validate:
- Missing DKIM signing on outbound mail
- Signature corrupted by intermediary
- DNS key record not published
- Selector mismatch
DMARC rejection
DMARC policy set to reject or quarantine, and alignment failed:
- SPF domain doesn’t align with From header
- DKIM domain doesn’t align with From header
- Neither mechanism passes
Relay denied
For organizations using SMTP relay services (including Gmail’s relay):
- Authentication credentials invalid or missing
- Sending IP not registered in relay configuration
- Relay requires SMTP AUTH but client sent unauthenticated
Content or attachment policy
Some 5.7.0 rejections stem from content filtering:
- Blocked attachment types
- Links to blacklisted domains
- Content patterns matching spam signatures
How do you fix 550 5.7.0?
Since 5.7.0 is generic, you’ll need to systematically check potential causes.
Verify SPF
Check your SPF record covers all sending sources:
dig TXT yourdomain.com | grep spf
Confirm:
- Record exists and has a valid syntax
- All sending IPs are authorized (include your ESP, CRM, marketing tools)
- DNS lookups stay under 10
- Record ends with ~all (softfail) or -all (hardfail)
Use the SPF lookup tool to validate your record.
Verify DKIM
Ensure DKIM signing is active:
- Check your email service’s DKIM settings
- Verify the public key is published in DNS
- Test by sending to a DKIM verification service
Use the DKIM lookup tool to confirm your key is accessible.
Verify DMARC
Check your DMARC policy allows delivery:
dig TXT _dmarc.yourdomain.comReview:
- Policy setting (p=none, p=quarantine, or p=reject)
- Alignment mode (relaxed or strict)
- Reporting addresses receiving failure reports
If using p=reject, ensure SPF or DKIM passes with proper alignment. Use the DMARC lookup tool to examine your record.
Fix relay configuration
If using an SMTP relay service:
Gmail SMTP Relay
- In Google Admin, navigate to Apps → Google Workspace → Gmail → Routing
- Verify allowed senders include your source IP
- Confirm authentication requirements match your client configuration
Microsoft 365
- Check inbound connectors in Exchange Admin Center
- Verify certificate name or source IP matches
- For hybrid environments, rerun the Hybrid Configuration Wizard
Check MX routing
Verify your domain’s MX records point to the correct servers:
- Use the MX lookup to confirm routing
- Ensure receiving servers are configured to accept mail for your domain
- Check for conflicting records
Contact recipient admin
If you’ve verified all authentication and the rejection persists:
- The recipient’s security policy may be overly restrictive
- Their admin can check security logs for specific rejection reasons
- Request whitelisting if legitimate business communication
How do you prevent this error?
Authentication and infrastructure hygiene prevent most 5.7.0 rejections.
Maintain authentication records
- Rotate DKIM keys periodically
- Monitor DMARC reports for failures
- Keep DNS lookup count under 10 for SPF
- Review SPF when adding new sending services
Test before bulk sending
Before launching campaigns from new infrastructure:
- Send test messages to major providers
- Verify authentication passes in headers
- Use an email deliverability test to check all providers
Document sending sources
Maintain a list of all systems sending as your domain:
- CRM systems
- Marketing platforms
- Internal mail servers
- Transactional email services
- Third-party tools with email notifications
When systems change, update authentication records immediately.
Still stuck after trying the fix?
Some email errors are easy to clear. Others point to deeper deliverability issues involving authentication, sender reputation, blacklisting, routing, or mailbox provider policy. If you would rather have an expert review it, speak with an email delieverability consultant for free and we can help diagnose the issue and fix it on your behalf.
We look beyond the error message itself to find what is actually breaking delivery, trust, or inbox placement.
From SPF, DKIM, and DMARC to blacklist cleanup, DNS alignment, and sending setup, we can guide or implement the fix.
We assess whether the error is part of a bigger pattern hurting opens, replies, and overall campaign performance.
Talk to a real deliverability expert, get honest guidance, and see the next best step without pressure or upsells.
When should you book a consultation? If the error keeps coming back, affects multiple mailboxes or domains, started after an ESP or DNS change, or is tied to spam placement, low inboxing, high bounce rates, or authentication failures, it is usually faster to get an expert involved early.
Frequently asked questions
Here are some commonly asked questions about this error:
The 5.7.0 code is a catch-all for security rejections that don’t fit specific enhanced codes. Some servers provide detailed text after the code explaining the exact policy violated — always read the full bounce message. Others keep it vague intentionally to avoid revealing their filtering logic.
Check the bounce text for keywords. Then send a test to a verification service (or your own address) and examine the Authentication-Results header — it shows pass/fail for each mechanism. DMARC aggregate reports also identify failure patterns.
Yes. Some organizations configure aggressive email security that rejects legitimate mail. If your authentication is correct and you still get 5.7.0, contact the recipient’s IT team. They may need to whitelist your domain or adjust their policy.
