Plain-language guides to the external security of your domains.https://perimetry.cloud/enhttps://perimetry.cloud/guides/brevo-dkim-dmarc/https://perimetry.cloud/guides/brevo-dkim-dmarc/Add the Brevo code, the two DKIM records and the DMARC record, keep your own DMARC reports, and check that Brevo signs your campaigns with your domain.Sat, 14 Nov 2026 00:00:00 GMTE-mailhttps://perimetry.cloud/guides/cyber-essentials-from-outside/https://perimetry.cloud/guides/cyber-essentials-from-outside/Which Cyber Essentials requirements leave a trace anyone can see from the internet, how to check them before your assessment, and what the scheme does not cover.Sat, 14 Nov 2026 00:00:00 GMTMethodhttps://perimetry.cloud/guides/google-workspace-dkim-dmarc/https://perimetry.cloud/guides/google-workspace-dkim-dmarc/Turn on DKIM in the Google Admin console, publish the right SPF and DMARC records, check that mail really passes, and avoid the usual errors.Sat, 14 Nov 2026 00:00:00 GMTE-mailhttps://perimetry.cloud/guides/mailchimp-dkim-dmarc/https://perimetry.cloud/guides/mailchimp-dkim-dmarc/Add the two CNAME records and the DMARC record Mailchimp asks for, check that your campaigns are signed with your own domain, and keep DMARC from breaking them.Sat, 14 Nov 2026 00:00:00 GMTE-mailhttps://perimetry.cloud/guides/microsoft-365-dkim-dmarc/https://perimetry.cloud/guides/microsoft-365-dkim-dmarc/Publish the two DKIM CNAME records Microsoft 365 asks for, turn signing on in the Defender portal, add SPF and DMARC, and check a real message.Sat, 14 Nov 2026 00:00:00 GMTE-mailhttps://perimetry.cloud/guides/passive-vs-active-scanning/https://perimetry.cloud/guides/passive-vs-active-scanning/The difference between a passive audit and an active vulnerability scan, what each can and cannot see, the risks of active testing, and how to combine them safely.Fri, 13 Nov 2026 00:00:00 GMTMethodhttps://perimetry.cloud/guides/attack-surface-monitoring/https://perimetry.cloud/guides/attack-surface-monitoring/What an attacker sees of your company from outside before trying anything, the seven areas worth watching, how often to look, and how to do it without a security team.Thu, 12 Nov 2026 00:00:00 GMTMethodhttps://perimetry.cloud/guides/dmarc-p-none-to-reject/https://perimetry.cloud/guides/dmarc-p-none-to-reject/The safe path to an enforced DMARC policy: what to check at each step, how pct and sp work, how long to wait, and what to do when a legitimate service fails.Thu, 12 Nov 2026 00:00:00 GMTE-mailhttps://perimetry.cloud/guides/exposed-ports/https://perimetry.cloud/guides/exposed-ports/Which services should never answer the whole internet, how attackers find them in minutes, how to see your own exposure without a scan, and how to close each one.Thu, 12 Nov 2026 00:00:00 GMTWebhttps://perimetry.cloud/guides/mta-sts-and-tls-rpt/https://perimetry.cloud/guides/mta-sts-and-tls-rpt/Why encryption between mail servers can be silently removed, how an MTA-STS policy and TLS reports prevent and reveal it, and how to set both up in an afternoon.Thu, 12 Nov 2026 00:00:00 GMTE-mailhttps://perimetry.cloud/guides/nis2-for-small-companies/https://perimetry.cloud/guides/nis2-for-small-companies/Who NIS2 covers, the difference between essential and important entities, the ten security measures, the 24-hour reporting rule and where to start this month.Thu, 12 Nov 2026 00:00:00 GMTMethodhttps://perimetry.cloud/guides/reading-dmarc-reports/https://perimetry.cloud/guides/reading-dmarc-reports/What the XML files from Google, Microsoft and others contain, how to tell your own services from forgers, and which rows to fix before moving to p=reject.Thu, 12 Nov 2026 00:00:00 GMTE-mailhttps://perimetry.cloud/guides/secrets-leaked-on-github/https://perimetry.cloud/guides/secrets-leaked-on-github/Why passwords and keys end up in public repositories, how attackers find them within minutes, and the order to act in: revoke first, clean the history second.Thu, 12 Nov 2026 00:00:00 GMTMethodhttps://perimetry.cloud/guides/supplier-security-nis2/https://perimetry.cloud/guides/supplier-security-nis2/What Article 21 expects about your suppliers, how to list the ones that matter, what you can check from outside without asking, and when to send a questionnaire.Thu, 12 Nov 2026 00:00:00 GMTMethodhttps://perimetry.cloud/guides/certificate-transparency-monitoring/https://perimetry.cloud/guides/certificate-transparency-monitoring/Every public certificate is recorded in a public log. How to use those logs to find forgotten subdomains, catch unexpected issuance and see expiry coming.Tue, 03 Nov 2026 00:00:00 GMTCertificateshttps://perimetry.cloud/guides/dnssec-and-caa/https://perimetry.cloud/guides/dnssec-and-caa/What DNSSEC protects against and why a broken deployment is worse than none, how a CAA record limits who can issue certificates for your domain, and how to turn both on.Tue, 03 Nov 2026 00:00:00 GMTDNShttps://perimetry.cloud/guides/look-alike-domains/https://perimetry.cloud/guides/look-alike-domains/How typosquatting works, the ten ways attackers vary a domain name, why registration is the earliest warning you will get, and what to do when a look-alike appears.Tue, 03 Nov 2026 00:00:00 GMTLook-alikeshttps://perimetry.cloud/guides/security-headers/https://perimetry.cloud/guides/security-headers/Which HTTP response headers actually reduce risk, what each one protects against, the exact values to use, and the mistakes that make a Content-Security-Policy useless.Tue, 03 Nov 2026 00:00:00 GMTWebhttps://perimetry.cloud/guides/spf-dkim-dmarc-explained/https://perimetry.cloud/guides/spf-dkim-dmarc-explained/What the three e-mail authentication records do, how they fit together, and the exact records to publish so that nobody can send mail as your domain.Tue, 03 Nov 2026 00:00:00 GMTE-mailhttps://perimetry.cloud/guides/subdomain-takeover/https://perimetry.cloud/guides/subdomain-takeover/Why a DNS record pointing at a cloud service you stopped paying for lets a stranger publish under your domain, how to find such records and how to remove them.Tue, 03 Nov 2026 00:00:00 GMTSubdomains