DNS Misconfiguration Check
DNS misconfigurations affect email deliverability and security. SPF, DKIM, and DMARC must be correctly configured to prevent spoofing and ensure mail reaches inboxes. This guide explains how to check your DNS configuration and fix common issues.
What Is DNS Misconfiguration?
DNS records control how your domain resolves and how email is authenticated. Misconfigured SPF, DKIM, or DMARC can cause legitimate mail to fail, land in spam, or allow attackers to spoof your domain. Missing or incorrect records are common when domains are newly set up, when email infrastructure changes, or when third-party services (CRM, marketing tools) are added without updating DNS.
Email spoofing is a major risk when SPF and DMARC are weak or absent. Attackers can send mail that appears to come from your domain, enabling phishing and business email compromise. Recipients and spam filters have no reliable way to distinguish spoofed mail from legitimate mail without proper authentication. A DNS misconfiguration check helps identify these gaps before they are exploited.
Key DNS Records for Email
- SPF: Specifies which servers can send mail for your domain. Prevents unauthorized senders.
- DKIM: Cryptographic signature for email authenticity. Verifies mail was not tampered.
- DMARC: Policy for handling SPF/DKIM failures. Tells receivers what to do with failing mail.
Common DNS Misconfiguration Issues
SPF record too permissive: Using ~all or ?all instead of -all weakens enforcement. Multiple SPF records cause validation failure (only one SPF record per domain). Exceeding the 10-lookup limit breaks SPF. Missing include for third-party senders (e.g. SendGrid, Mailchimp) causes legitimate mail to fail.
DKIM selector mismatches: The selector used when signing must match the one receivers query. Wrong selector or missing record causes DKIM to fail. DMARC policy at none (p=none) provides monitoring only; move to quarantine or reject for real protection. Conflicting or duplicate records can cause unpredictable behavior.
Common Issues to Check
- SPF record exists and uses -all for strict enforcement
- All legitimate mail senders included in SPF
- DKIM selector and record match your mail provider
- DMARC policy is quarantine or reject, not just none
How to Check DNS Configuration
Use Vulnify's DNS checker to validate SPF, DKIM, DMARC, and related records. Enter your domain to get a detailed report with missing records, syntax errors, and policy issues. The checker identifies which senders are authorized, whether DKIM is signing, and what happens to failing mail.
Run the check after any change to email infrastructure: adding a new CRM, switching email providers, or setting up transactional mail. Re-check periodically as providers update their requirements. For manual verification, use dig or nslookup to query TXT records; Vulnify's tool automates this and interprets the results.
Check Checklist
- Verify SPF record exists and includes your mail servers
- Confirm DKIM is configured and signing
- Check DMARC policy (none, quarantine, reject)
- Ensure no conflicting or duplicate records
How to Fix DNS Misconfiguration
Fix SPF by adding all legitimate sending IPs or includes. Use include: for third-party providers. End with -all for strict fail. Fix DKIM by ensuring your mail provider's signing is enabled and the public key is published at the correct selector. Fix DMARC by publishing a policy record; start with p=none for monitoring, then move to p=quarantine and p=reject as you gain confidence.
Remediation Priority
- SPF: Add missing senders; use -all for fail
- DKIM: Enable signing; verify selector matches
- DMARC: Publish policy; move from none to reject
Frequently Asked Questions
How do I check my DNS?
Use Vulnify's free DNS checker. Enter your domain to get SPF, DKIM, DMARC, and DNSSEC analysis with remediation guidance.
Why is my mail going to spam?
Missing or weak SPF, DKIM, or DMARC can cause deliverability issues. Run a DNS check to identify gaps and fix them.
What is the 10-lookup limit for SPF?
SPF allows up to 10 DNS lookups (includes, a, mx, etc.). Exceeding this causes permanent failure. Consolidate with fewer includes or use subdomains.