- HTTPS / TLS
- Encryption between the browser and your server so data can't be read or altered in transit — the padlock.
- HSTS
- A header (Strict-Transport-Security) that forces browsers to always use HTTPS for your site, even if someone types http.
- CSP
- Content-Security-Policy — a header that whitelists what may load on your page, blocking most cross-site scripting.
- X-Frame-Options
- Stops other sites embedding yours in a hidden frame to trick your users into clicking (clickjacking).
- SPF
- A DNS record listing who may send email for your domain — the first defence against spoofed mail.
- DKIM
- A cryptographic signature on outgoing email that lets receivers verify it genuinely came from you.
- DMARC
- A DNS policy telling receivers what to do with mail that fails SPF/DKIM — and that emails you abuse reports.
- Mixed content
- Loading some resources over plain HTTP on an HTTPS page — it breaks the padlock and can be intercepted.
- Cookie flags
- Secure, HttpOnly and SameSite settings that stop session cookies being stolen by scripts or sent insecurely.
- End-of-life (EOL) software
- A CMS, plugin or runtime past its support date — no more security patches, so known exploits keep working.
- DNSSEC
- Cryptographic signing of your DNS so attackers can't forge where your domain points.
- CAA
- A DNS record naming which certificate authorities may issue HTTPS certificates for your domain.