postfix MTA questions

[dave]

Hello,
    I'm using postfix and i've got two questions regarding it. Firstly, i'd
like to implement maildir style mailboxes for users. I want a pop server
that will understand maildir, will qpopper do this or will i have to look at
another? I'd like to avoid running services from inetd if possible.
    I'm also wondering if there's a program that will take an incoming
message, and send back an autoresponse asking for confirmation before
delivery? If a confirmation is sent, the message is not spam, and is sent
through, if no confirmation is forthcoming within a time frame or if the
domain bounces the message both the original message and any domain bounces
are perged without me seeing them.
    Finally, I've got a domain on a dynamic IP, i'd like to relay through my
isp's smtp server as a smarthost, if i do this will my outgoing domain name
be altered?
Thanks.
Dave.