Free password, DNS and e-mail security tools

DNS

Look up records and compare answers across resolvers.

• DNS Lookup See the DNS records a domain publishes, with TTLs and an explanation of each record type.
• MX Lookup Find the mail servers that receive e-mail for a domain, in the order senders try them.
• DNS Propagation Checker Compare the same record across major public resolvers and the domain's authoritative name servers.

Domains & IP addresses

Find who registered a domain or IP range, reverse DNS and your own IP.

• WHOIS Lookup See a domain's registrar, registration and expiry dates, status codes and name servers, straight from the registry.
• IP WHOIS Lookup Find out which organisation an IP address range is registered to, and where to report abuse.
• Reverse IP Lookup Find the host name behind an IP address (PTR record) and check that it points back to the same address.
• What Is My IP Your public IP address as websites see it, with its reverse DNS host name.

E-mail authentication & delivery

Check SPF, DKIM, DMARC, blocklists and message headers.

• SPF Checker Validate a domain's SPF record, expand every include, and count DNS lookups against the limit of 10.
• DMARC Checker Find a domain's DMARC policy, check its syntax and see in plain language what receivers will do with failing mail.
• DKIM Lookup Check the DKIM public key published for a selector, including key type, size and flags.
• Blacklist Checker Check whether an IP address, or the servers behind a domain, appear on public DNS blocklists.
• Email Header Analyzer Paste a message's raw headers to see where it came from, how long each hop took and whether it passed authentication.
• MTA-STS & TLS-RPT Checker Check that sending servers are told to deliver your mail only over verified TLS, and that you receive TLS failure reports.
• BIMI Checker Check whether your brand logo can appear next to your e-mails in Gmail, Yahoo and Apple Mail.

Web & TLS

Inspect certificates, response headers and redirects.

• SSL Certificate Checker Check a server's TLS certificate: whether it is trusted, matches the host name and how long until it expires.
• HTTP Header Checker See the response headers a web page returns and how its security headers are set up.
• Redirect Checker Follow a URL through every redirect and see each status code and destination.

Guides

Practical answers, each linked to the tool that checks it.

• How to set up SPF, DKIM and DMARC: a step-by-step guideSet up SPF, DKIM and DMARC for your domain in the right order: list your senders, publish records, verify with free checkers and move DMARC to enforcement.
• Moving DMARC from p=none to p=reject without losing mailA practical plan for moving DMARC from p=none to quarantine and reject: read aggregate reports, fix failing senders, handle subdomains and forwarding.
• Gmail, Yahoo and Outlook bulk sender requirements: the 2026 checklistWhat Gmail, Yahoo and Outlook.com require from senders in 2026: SPF, DKIM, DMARC, alignment, one-click unsubscribe, spam-rate limits and how to check each item.
• Is my IP or domain blacklisted? How to check and get delistedHow to check whether your mail server IP or domain is on a DNS blocklist, what a listing means, how to fix the cause and request removal.
• How long does DNS propagation take? TTLs and caching explainedDNS propagation is really cache expiry. How TTLs, negative caching and name-server changes decide how fast a DNS change shows up, and how to speed it up.
• How to read e-mail headers and spot phishingLearn which e-mail headers to trust, how to read Received lines and Authentication-Results, and the warning signs of phishing — with a free header analyzer.

All guides →