Fix DKIM: use relaxed/relaxed canonicalization, reject non-FQDN senders#572
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Fix DKIM: use relaxed/relaxed canonicalization, reject non-FQDN senders#572
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DKIM signing: Changed from simple/simple (library default) to relaxed/relaxed canonicalization. Google is strict about whitespace — simple mode causes verification failures if any mail processor touches header or body whitespace in transit. Also added explicit HeaderKeys list (from, to, subject, date, message-id, mime-version, content-type) instead of signing all headers, which is more predictable. SMTP sender validation: The inbound SMTP server was accepting mail from addresses like "no-reply@wetransfer" — that's not a valid FQDN (no dot in the domain). Added three validation checks before the existing anti-spoofing and blocklist: 1. Address must parse (mail.ParseAddress) 2. Must have a non-empty domain after @ 3. Domain must contain a dot (FQDN check) Rejects with 550 and logs the specific reason. https://claude.ai/code/session_01GRGLA9yj7BpqKiyi6xFwnm
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DKIM signing:
Changed from simple/simple (library default) to relaxed/relaxed canonicalization. Google is strict about whitespace — simple mode causes verification failures if any mail processor touches header or body whitespace in transit. Also added explicit HeaderKeys list (from, to, subject, date, message-id, mime-version, content-type) instead of signing all headers, which is more predictable.
SMTP sender validation:
The inbound SMTP server was accepting mail from addresses like "no-reply@wetransfer" — that's not a valid FQDN (no dot in the domain). Added three validation checks before the existing anti-spoofing and blocklist:
Rejects with 550 and logs the specific reason.
https://claude.ai/code/session_01GRGLA9yj7BpqKiyi6xFwnm