Free email and DNS security tools
Quick, single-purpose checks you can run on any domain. No sign-up. Each one reads public DNS or one public file, nothing more.
SPF lookup counter
Follows every include: and counts the DNS lookups an SPF record needs, against the limit of 10.
DMARC record explainer
Paste a DMARC record and read what each tag tells mail providers to do, in plain English.
MTA-STS checker
Checks the _mta-sts record, the policy file, its mode, max_age, MX coverage and TLS reporting.
Guides that pair with these tools
Guide
SPF, DKIM and DMARC explained: the complete guide for MSPsHow the three email authentication records fit together, with real examples, alignment explained and a rollout plan that does not break mail.
SPF too many DNS lookups
The SPF 10-lookup limit: why adding one more email tool breaks itWhy SPF silently fails after a few include: entries, how to count lookups, and how to fix it without breaking mail.
MTA-STS setup
MTA-STS in 10 minutes for Microsoft 365 and Google WorkspaceTwo DNS records and one small text file make other mail servers encrypt email sent to you. Copy-paste setup inside.