Re: [PATCH] wip: Add forward-message-refs function.

Hi,
 
Alejandro Colomar via Mutt-dev <[email protected]> writes:
>> Because that would be invalid. A mail thread is a tree; 
>> References: describes a path through a tree, like a pathname of 
>> a file. In a tree, a node can only have one parent. Message 
>> threads, being trees, do not allow multiple parents. 
> 
> This is allowed.  In-Reply-To can have more than one message 
> IDs.  Quoting RFC 5322: 
> 
> 	The "References:" and "In-Reply-To:" fields each contain 
> one or more unique message identifiers, optionally separated by 
> CFWS. 
> 
> I have personally used this one or two times, when replying to 
> more than one message at once.  I suspect that --since I did it 
> manually--, I got the References from only one of them, but I 
> don't remember. 
> 
> Out of curiosity, I've grepped for all mails that have something 
> like that in my maildir: 

JFYI, this was discussed in the IETF working group during the work 
on either 2822 or 5322, I think it may have been in 2003 or 2004 
but don't hold me to that.

A mail thread is not necessarily a tree. Many people want it to 
be, much software expects it to be, but that relies on cooperation 
by everyone, and some email software doesn't cooperate. You can 
say it's a DAG, but I've even seen cycles.

Some people DO send a single message that replies to several other 
messages in a thread. Fact of life. Like it or not.

The cycles are due to bugs or attacks, I think, but the DAG nature 
is due to intentional behaviour.

The conclusion at the time was twofold. ① In-Reply-To should name 
all the messages to which this message is a direct reply. ② 
References should contain the References of the message being 
replied to and Message-Id of that message, if this message is a 
reply to a single message. ③ There is no specified algorithm for 
constructing References for a message that is a reply to several 
messages. I think someone mentioned a MUA that can construct such 
replies, one with a four-letter abbreviation as name, but nobody 
wanted to discuss this in detail or standardise it. Yes, this is 
the third point in a two-point list, and it's a no-op.

Arnt