On Mon 24/Mar/2025 20:49:32 +0100 Wei Chuang wrote:
To support that use case and other scenarios where the recipient is not
explicitly declared in the RFC5322 message e.g. some mailing lists, the sender
can populate a DKIM2-Signature "rt=" tag. Note that "rt=" here still only
supports a single recipient.
Why such single recipient limitation?
Sender Example::
header:
To: user....@example.com
Cc: user....@example.com
DKIM2-Signature: h=to:cc
To: user....@example.com, user....@example.org
Cc: user....@example.com
DKIM2-Signature: rt=user....@example.com:user....@example.com
Now SMTP in the transaction with example.com's MX stays the same:
SMTP
RCPT TO: user....@example.com <mailto:user....@example.com>
RCPT TO: user....@example.com <mailto:user....@example.com>
That assumes the MTA is DKIM2-aware. If you don't have that, you're better off
splitting all messages to single recipient.
Best
Ale
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