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Re: "proper" handling of BCC

2012-02-29 18:09:12

At 9:18 AM -0800 2/29/12, <ned+ietf-smtp(_at_)mrochek(_dot_)com> wrote:

 Absent an extension, the MUA has no way of knowing if this parameter even
 exists in the MSA, let alone how it is set.

Yes, exactly.

 That's another reason why you need an extension - you absolutely do need a
 parameter so that the MSA only does this stuff if the MSA requests it.

Yes, exactly.

 I also think this is the wrong way for it to work. The problem with
 this approach is that it forces the MSA to parse and modify headers,
 and compare the addresses extract from those headers with the
 various envelope addresses. That's inherently risky.

Yes, exactly.

It's much safer to have the MUA send a message without any of these headers in
 it and to have the MSA simply add the Bcc: field to message copies as needed.
 This can be done with a BCC parameter on the RCPT TO:. The value of that
 parameter can be the personal name phase to add to the address. This
 way the only thing the MSA has to do is decode the parameter value,
 concatentate some strings and add a header field containing the result.

 Alternately, the value of the BCC parameter could be the entire Bcc: field
value. This would provide support for stuff like group constructs, assuming we
 want to allow that. (I can argue it either way.) This is even simpler because
 now all the MSA has to do is decode the parameter and stuff it into a new
 header field.

Two good approaches.

 Remember, the target audience here has to be more than just a bunch of
 geeks or this doesn't stand a chance of deploying.


The most useful thing, in my view, is a BCP on how MUAs should generate messages with BCC recipients, and how MUAs should recognize when a received message is a result of a BCC, and how to handle replies etc. in such cases.

I'm intrigued by the behavior mentioned earlier of the originating MUA mucking with the To and Cc header fields when sending a BCC version, as an indication of this and to avoid unthinking reply-to-all actions. I'm not sure I'm a huge fan of the "[To:]" business, but enclosing the contents in parens to form a comment might work.

Randall Gellens
Opinions are personal;    facts are suspect;    I speak for myself only
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