J,
I argued that the argument was backwards, and that, conversely, it's
emails that are more permanent than the web archive. Messages in the
web archive can be deleted, but anyone who receives an email can keep
it for as long as they want to, and deletion of a group message does
nothing to affect that.
I agree with all of that.
The description of the emails as being "fleeting" can be misleading. The message itself isn't fleeting, as you correctly point out it may be retained by the recipient indefinitely.
Which is why I say availability is more the issue than permanence. The messages kept in email folders, permanently or not, don't matter because they are not available to others. Those kept in the Messages section on the web though are available to all current and future members (deletion aside). And in the case of a group with public archives available to everyone.
Shal
Shal Farley