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Restore Aggressive LMTP header cleanup #1005

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Restore Aggressive LMTP header cleanup #1005

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26 changes: 23 additions & 3 deletions cmdeploy/src/cmdeploy/postfix/lmtp_header_cleanup
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Original file line number Diff line number Diff line change
@@ -1,3 +1,23 @@
/^DKIM-Signature:/ IGNORE
/^Authentication-Results:/ IGNORE
/^Received:/ IGNORE
# List of headers for incoming messages
# that must be retained for functionality and compatibility reasons
/^From:/ DUNNO
/^Message-Id:/ DUNNO
/^Chat-/ DUNNO
/^Content-Type:/ DUNNO

@link2xt link2xt Jul 22, 2026

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For safety i'd list all "Structural headers":

  • MIME-Version
  • Content-Type
  • Content-Transfer-Encoding
  • Content-Disposition

Removing Content-Transfer-Encoding from multipart MIME message sounds dangerous regardless of the signatures on the message.


# For receiving clear-text messages (still supported in May 2026)
/^Subject:/ DUNNO
/^Date:/ DUNNO
/^To:/ DUNNO
/^CC:/ DUNNO
/^References:/ DUNNO
/^In-Reply-To:/ DUNNO

# Senders might support Autocrypt 1 but not RFC9788 (Header Protection)
/^Autocrypt:/ DUNNO

# SecureJoin V2 protocol headers (for backward compatibility)
/^Secure-Join/ DUNNO

# Ignore all other headers
/.*/ IGNORE