The 550 5.7.30 error means the receiving server rejected your email because DKIM signature validation failed — the cryptographic signature in your email didn’t match the public key in DNS, or no valid signature existed.
Fix it by verifying your DKIM TXT record is correctly published, ensuring your mail server signs outgoing messages, and confirming the public key matches what your email service provides.
DKIM failures indicate either DNS misconfiguration or signing problems at the mail server level. Unlike SPF (which checks sending IPs), DKIM verifies message integrity — a failed signature suggests tampering or misconfiguration, both of which are concerning signals to receiving servers.
Quick skim — 550 5.7.30 error overview
The 550 5.7.30 error indicates DKIM-specific authentication failure.
| Attribute | Details |
| Error code | 550 5.7.30 |
| Category | Authentication/signature failure |
| Meaning | DKIM signature invalid or missing |
| Severity | Permanent (requires DNS and server configuration) |
| Common causes | Missing DNS record, signing disabled, key mismatch |
| Fix approach | Verify DNS record → enable signing → test validation |
If you’re seeing broader DKIM failures beyond this error code, see our full guide on DKIM Fail Explained.
How do you fix a DKIM authentication failure?
Systematic verification identifies whether the problem is DNS, signing, or both.
Verify the DKIM record exists
Check DNS for your DKIM public key:
dig TXT selector1._domainkey.yourdomain.comReplace selector1 with your actual selector (provided by your email service). Use the DKIM lookup tool for automated checking.
The response should include a TXT record starting with v=DKIM1; containing your public key.
Get the correct record from the provider
Each email service provides specific DKIM records:
- Google Workspace: Admin Console → Apps → Gmail → Authenticate email
- Microsoft 365: Defender portal → Email authentication → DKIM
- SendGrid, Mailgun, etc.: Dashboard → Domain authentication settings
Copy the exact TXT record value (including selector name) from your provider.
Add/update DNS record
In your DNS provider’s control panel:
- Create a TXT record
- Host/Name: selector._domainkey (selector from provider)
- Value: The full public key string from the provider
For long keys, some DNS providers require splitting across multiple strings or have specific formatting. Check provider documentation.
Verify key format
Common formatting issues:
- Missing v=DKIM1; prefix
- Missing p= before the public key
- Extra whitespace or newlines in the key
- Key truncated by character limits
The record should look like:
v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GN...Enable signing on the mail server
For self-hosted mail servers, verify DKIM signing is active:
- Postfix with OpenDKIM: Check /etc/opendkim.conf and signing table
- Exchange: Enable DKIM in Exchange Admin Center
- Cloud providers: Enable in the authentication settings dashboard
Wait for propagation
After DNS changes:
- Allow 15-60 minutes for initial propagation
- Some resolvers cache for longer
- Test from multiple locations if results are inconsistent
Test validation
Send a test message and verify DKIM passes:
- Send to a Gmail account and check Authentication-Results header
- Use verification services (mail-tester.com, etc.)
- Run a email deliverability test
How do you prevent DKIM failures?
DKIM requires maintenance during infrastructure changes and key rotation.
Document key configuration
Track for each sending domain:
- Selector name
- Key publication date
- Which service uses which selector
- Key rotation schedule
Monitor authentication
Check DMARC aggregate reports for DKIM failures. Sudden increases indicate:
- DNS record issues
- Signing configuration changes
- Unauthorized senders attempting to spoof
Rotate keys periodically
DKIM keys should rotate annually (or more frequently for high-security environments):
- Generate a new key pair with a new selector
- Publish new public key in DNS
- Update signing configuration to use the new selector
- Keep the old selector active during transition
- Remove the old selector after propagation
Test after changes
Any change to the mail infrastructure warrants DKIM verification:
- Provider migrations
- Server updates
- DNS provider changes
- Domain registrar transfers
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:
SPF verifies where the email comes from (which IP addresses are authorized). DKIM verifies what the email contains (message integrity via cryptographic signature). Both contribute to DMARC evaluation, but they check different things.
Third-party services sign with their own domain by default (d=sendgrid.net), which doesn’t align with your From domain for DMARC. Configure custom DKIM with your domain through the provider’s authentication settings — they’ll give you a TXT record to publish.
Yes. If a forwarding service modifies headers or body content included in the DKIM signature, validation fails at the final destination. Mailing lists that add footers commonly cause this. DMARC’s fallback to SPF helps, but neither may pass for heavily modified forwards.
Your email service provider specifies the selector. Check their documentation or admin dashboard. Common patterns include selector1, google, s1, or provider-specific names. The selector in your DNS record must match what your mail server uses when signing.
