I understand fully all the different ways you could do this.
What your suggesting is no different then creating a second yahoo group to backup messages from the first.
Pretty frickin pointless.
How do you reply to messages? Users on your board may not be on the yahoo group list.
All the messages will appear to come from the same exact person.
If messages are editted or email chains deleted from the yahoo group, they will not be deleted on your forum. So you have massive information discrepancies there as well.
I'll say it one more time
This modification is NOT made to work WITH a mailing list.
It is made to BE a mailing list in and of itself!
It turns one of your forums... into a mailing list.
Any attempts to integrate with an existing group mailing list, like yahoo groups, will create major discrepancies, errors and confused users.
If you want to backup information from a mailing list... search google. There are download programs for just about every free mailing list to make backups of the messages.
I'm sorry to be so abundantly blunt but I don't seem to be getting the message across.
*hugs*