"Foundational" business software

> It should be that, if you're using LDAP, and using the agreed-upon 
> schema, any mail server software you happen to pick will need no 
> modification from the defaults for configuration.

That is extremely unlikely to happen.

>Furthermore, all mail clients will be able to find the user's mail, again 
>with no configuration changes.

Multiple standards for this already exist: SLP, DNS SRV, and Rendevous (there is some overlap
among these).  Unfortunately almost no clients support them; and no Open Source client that
I'm aware of.  Partly this is because people want to setup multiple custom accounts whereas a
client supporting these would have more of a locate-my-imap-and-smtp-servers mentality.

> doing the same thing, and inform spam filter software. All of the 
> representation decisions that are currently made within projects and 
> not publicized to other projects would be made explicitly and in a 
> forum where other projects' decisions are findable, and where the group
> consensus, once one forms, is clear.

This is generally what a projects commit log and devel mailing list are.  But that doesn't
help create a standard whereby application X can understand the intent of an action performed
by application Y;  without a central broker and standard that isn't going to happen.