On Wed, Aug 9, 2023 at 2:54 AM Laura Atkins <la...@wordtothewise.com> wrote:
> It seems to me there is a lot of heavy lifting to be done to make sure > that the individual recipient only sees a copy of the message with their > address in the BCC header. > > If there are multiple BCCs that implies that whatever is creating the mail > must make individual copies of the message with only the BCC recipient in > that line before it’s signed with DKIM. So for a message with 3 BCCs, there > are 4 separate copies of the message to be created, one with no BCC header > and 3 for each of the BCC recipients. Then each message must be > individually signed. > > I’m not sure how that’s going to work in practice. > +1. It also flies in the face of advice in RFC 5321 to curtail duplication of message instances. Of the three Bcc schemes described in RFC 5322, this one is the most expensive and complicated. I surmise that they were describing legacy behavior rather than encouraging a particular approach. -MSK
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