yeah I was away from the computer and I was just thinking about that too >>> DeltaSync is completely integrated into Windows Live Mail, and I doubt it could be redirected to a mail proxy.
As to Outlook, I haven't used it long enough to tell. Delta Sync isn't the only alternative for hotmail accounts (apart from POP), there's Microsoft Exchange...in Outlook 2010. Can't remember Avast mail shield behavior with it, but I don't think Avast can interfere with that either.
As to the Avast plugin, I couldn't try it as I'm on 64 bit. Thought the goal of was just to scan archived mails there...