Free DNS & Email Security Tools
No account required. Use these free tools to audit and improve your domain's email security and DNS configuration.
DNS Visualizer
Map SPF, DKIM, DMARC, and DNSSEC records visually. Instant DNS security audit.
DMARC Checker & Generator
Check your DMARC record or generate a new policy to prevent email spoofing.
SPF Record Checker
Validate SPF syntax, detect excessive lookups and missing -all policy.
MTA-STS Validator
Verify your MTA-STS DNS record and policy file for encrypted email delivery.
Bulk DNS Checker
Look up A, AAAA, MX, NS, CNAME, TXT, SOA, CAA records for multiple domains.
Email ROI Calculator
Calculate revenue lost to poor email deliverability and spam folders.
Common email & DNS error fixes
Step-by-step guides for Gmail rejections, SPF PermError, DMARC alignment, and more.
Fix Gmail 550 5.7.26 Authentication Required
Gmail rejected your message with 550 5.7.26 authentication required. Fix SPF, DKIM, DMARC alignment, and envelope-from settings in three steps.
Fix SPF PermError (Permanent Error)
SPF PermError means your SPF record is invalid or exceeds 10 DNS lookups. Remove dead includes, fix syntax, and validate before mail fails DMARC.
Fix DMARC Alignment Failed (SPF Passed)
DMARC alignment failed but SPF passed? Your envelope-from or DKIM domain does not match the visible From address. Diagnose and fix alignment in three steps.
Fix Gmail Unverified Sender Warning
Gmail unverified sender means missing DMARC or failed alignment. Publish DMARC, enable DKIM on M365 or ESP paths, and validate with the DMARC checker.
Fix SPF Too Many DNS Lookups
SPF records allow max 10 DNS lookups. Too many includes cause PermError and deliverability failures. Audit includes and validate with the SPF checker.
Need continuous monitoring?
ZeroHook automatically monitors your DNS configuration 24/7 and alerts you to changes, expiring certificates, and security issues before they affect your business.