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emersion/mailing-lists.md

Last active February 25, 2019 11:19
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mailing-lists.md

What does a mailing list need to do to reflect a message?

Method 1

Keep the original From header. Add a Sender header field with the list's address. Broadcast message with MAIL FROM set to the list's address.

Issues:

  • Bounces don't go to the list (they should because of Sender).
  • Can't add a prefix to Subject or a footer to body. No unsubscribe link, is this GDPR-compliant?
  • Breaks DMARC alignment for SPF (but SPF is legacy). If DKIM is also used it should be fine, except if the DMARC policy specifies fo=1 (requires both SPF and DKIM to pass).

Method 2

Replace From with the list, add Reply-To with the original From, strip DKIM. Broadcast message with MAIL FROM set to the list's address.

Issues:

  • Headers are messed up and don't make sense (From is not the real From).
  • Replies go to the list instead of the original author.

Extra stuff

  • Add List-* fields
  • Sign with the list's DKIM key

References

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