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there are two important problems in email

From: Kermit

  1. Make sure the message gets to the right recipient. This is what MX records are for.
  2. Make sure the sender didn’t lie about their From: address. This is what SPF, DKIM, and DMARC records are for.

SPF/DKIM/DMARC are very complicated but we’ll give a tiny incomplete summary.

MX records tell you the mail server for a domain

$ dig +short MX

5 is the priority is the server’s domain name

copy and paste your MX records

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person: you’re probably using an email service like Fastmail/Gmail, so just copy the records they tell you to use

tiny guide to SPF/DKIM/DMARC records

SPF: list of allowed sender IP addresses
Example: v=spf1 ip4: -all

DKIM: sender’s public key
Example: v=DKIM1; k=rsa; p=MIGFMA0GCSqGSI.......

DMARC: what to do about SPF/DKIM failures
Example: v=DMARC1; p=reject;

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