Pillar 017
Technical Setup & DNS
The keel beneath the waves. Dive deep into DNS, MX, A, and TXT records, the unseen framework that keeps your email vessel seaworthy. Misconfigured records are leaks waiting to happen.
Fundamentals of DNS for Email
- What is DNS?
- How does DNS relate to email?
- What are DNS records used for in sending and receiving mail?
- How does a DNS lookup work?
- What’s the difference between authoritative and recursive DNS?
- What is DNS propagation?
- How long does DNS propagation take?
- What is TTL (Time To Live) in DNS?
- What happens when a DNS record is misconfigured?
- How can DNS affect deliverability speed or reliability?
- What are TXT, MX, CNAME, and A records?
- Why do email services rely heavily on TXT records?
- What is DNS caching and how does it affect testing?
DNS Record Types (MX, A, TXT, CNAME)
- What is an MX (Mail Exchanger) record?
- How do MX records determine where mail is delivered?
- How do priority levels in MX records work?
- How do fallback MX servers function?
- What happens if your MX record is missing?
- What’s the difference between internal and external MX records?
- How to test MX resolution?
- How does MX misconfiguration affect inbound mail?
- Can a domain have multiple MX records?
- What’s the difference between MX and A record routing?
- How do third-party inbound filters (e.g., Proofpoint, Mimecast) modify MX setups?
- How do you update MX records safely without downtime?
- What is an A (Address) record?
- What is an AAAA record (IPv6)?
- What’s the difference between IPv4 and IPv6 in email delivery?
- What happens when an A record points to the wrong IP?
- What’s the difference between the sending IP and domain IP?
- What is a TXT (Text) record used for in email? (SPF, DKIM, DMARC, BIMI)
- What are TXT records?
- Why are TXT records used for email authentication?
- What is a “multi-string” TXT record?
- What’s the 255-character limit and how to handle it?
- How to flatten TXT records safely?
- How can multiple TXT records conflict?
- What’s the correct syntax for quotes and spaces?
- How do DNS providers differ in TXT handling?
- What happens if TXT records overlap (e.g., multiple SPF entries)?
- How can TXT formatting errors break authentication?
- How do TXT records interact with DMARC, SPF, and DKIM?
- How to check TXT records from the command line?
- What is a CNAME (Canonical Name) record?
- How do CNAMEs relate to link tracking?
- Why do ESPs use CNAMEs for click and open tracking?
- How does a branded tracking domain work?
- What’s the difference between link CNAME and email sending domain?
- What happens if your CNAME isn’t verified?
- How do you set up link branding in ESPs?
- How can unbranded tracking hurt deliverability?
- How can broken CNAMEs cause reputation issues?
- How to test if your tracking domain is working?
- What are common CNAME misconfigurations?
- How do these records work together for email delivery?
Reverse DNS (PTR Records)
- What is Reverse DNS (rDNS)?
- What is a PTR (Pointer) record?
- What’s a PTR record (reverse DNS) and why is it important?
- Why is a valid PTR record important for email deliverability?
- How does rDNS affect email authentication?
- How do I set up a PTR record for my sending IP?
- Does my hostname need to match my rDNS lookup? (Forward-confirmed reverse DNS - FCrDNS)
- How does rDNS mapping confirm sender identity?
- How do ISPs use reverse DNS in trust scoring?
- How to check and verify PTR alignment?
- What happens if PTR and HELO don’t match?
DNS Management & Propagation
- Where do I manage my DNS records? (e.g., domain registrar, hosting provider, DNS service)
- How can I check if my DNS records have propagated?
- What’s the difference between registrar and DNS host?
- How do you delegate DNS management?
- What’s the impact of using Cloudflare, GoDaddy, or Route53 for email DNS?
- How can DNS host limitations break authentication?
- What are “hidden” DNS editors and record propagation delays?
- How to migrate DNS between providers without downtime?
- How to maintain version control of DNS settings?
- What are the best practices for naming and documentation?
- How to set up alerts for DNS record changes?
DNS Limits & Flattening
- What are the common DNS limitations for email records? (e.g., SPF lookups, TXT record length)
- How does the SPF 10-lookup limit work technically?
- What happens if I exceed DNS limits?
- What is SPF flattening and how does it help?
- Are there risks associated with SPF flattening?
- Are there limits on the number of TXT records per domain?
DNS Checkers & Tools
- What online tools can I use to check my MX records?
- What tools check SPF records?
- What tools check DKIM records?
- What tools check DMARC records?
- What tools check PTR records?
- How do you test DNS propagation?
- What’s the difference between online testers and command-line tools?
- How to use dig, nslookup, or host for DNS testing?
- How do you verify all authentication records (SPF, DKIM, DMARC, BIMI)?
- How do you read DNS query results accurately?
- How to troubleshoot SPF “permerror” or “temperror”?
- How to identify TXT record conflicts?
- How to debug DKIM signature fails?
- How to identify DNS caching delays?
- What are the most common misconfigurations seen in deliverability audits?
- How to monitor DNS changes over time?
TTL Strategy
Split-brain DNS Pitfalls
DNSSEC & Security Enhancements
- What is DNSSEC?
- How does DNSSEC protect email authentication?
- What’s the difference between DNSSEC and SSL/TLS?
- What is a DNS signature (RRSIG)?
- How does DNSSEC prevent spoofing or hijacking?
- Do all DNS providers support DNSSEC?
- What happens if DNSSEC is misconfigured?
- How can DNSSEC affect DKIM verification?
- Should small businesses enable DNSSEC?
- How can you test DNSSEC deployment?
DNS & Deliverability Correlations
- Can DNS speed or latency affect inboxing?
- What happens when DNS lookups time out during delivery?
- How do DNS errors contribute to throttling or retries?
- What DNS issues commonly cause “no reverse DNS” rejections?
- How does DNS hosting location affect delivery speed?
- How does DNS TTL tuning improve email reliability?
- Can DNS outages lead to false bounce spikes?
- How do mail filters cache DNS data for spam analysis?
- What’s the connection between DNS trust and sender reputation?
- How can DNS transparency influence anti-spoofing trust models?
DNS Myths & Misunderstandings
- Is DNS setup “one and done”?
- Do SPF and DKIM work without proper DNS?
- Can TXT records be added in any order?
- Does DNSSEC automatically improve deliverability?
- Does flattening SPF always fix errors?
- Can you have multiple DMARC records?
- Does BIMI guarantee inbox placement?
- Do DNS propagation delays affect real-time sending?
- Is reverse DNS optional for bulk senders?
- Can Cloudflare break email DNS setups?
Trust beats tactics.
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