Certificate expiry, email spoofing protection, DNS setup and security headers — all checked at once. No signup, nothing to install.
If visitors cannot open the site, check DNS, the certificate and the redirect destination first. If outgoing mail fails, inspect SPF, DKIM and DMARC together. If the site works and only a header is missing, review what that header would change before deploying it. These are different problems and should not be treated as equally urgent.
Only public information is read (DNS records, certificates, HTTP responses). Nothing is logged in, and no load is placed on the site.