$ ls ./systems-administration
Systems Administration
Showing 11 of 11.
Email deliverability checklist
Reverse DNS, SPF, DKIM, DMARC, MTA-STS and blocklists, what each one actually does and the order to fix them in.
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MX records for mail delivery
What MX records do, how priorities work and why a second one is worth publishing.
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Reverse DNS for mail servers
PTR records, forward confirmed reverse DNS, and why you set them at your hosting provider.
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SPF records explained
Publishing SPF, choosing between ~all and -all, and the mistakes that switch it off completely.
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The SPF ten lookup limit
Why SPF silently stops working once the record needs more than ten DNS lookups, and how to get back under it.
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DKIM signing explained
How DKIM signatures work, what a selector is, and why a checker cannot always find your key.
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Rolling out a DMARC policy
From p=none to p=reject without blocking your own mail, and what the reports are actually for.
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MTA-STS and TLS reporting
Requiring TLS for inbound mail, and getting told when it fails.
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DNSSEC for mail
Why signing your zone matters when everything else you publish lives in DNS.
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STARTTLS and MX certificates
Encrypting mail in transit, and what a certificate name mismatch on an MX actually costs you.
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Mail server blocklists
How DNSBLs work, what to do if you are listed, and why a checker sometimes cannot tell you.
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