Some help with e-mail setup

["Kieren Diment" <kieren@mailandnews.com>]

I am in the process of setting up my laptop to work with Debian as 
a home dial-up computer.  Now that I have apm and pcmcia 
working together, I would like to be able to get the e-mail system 
working so I don't have to reboot to windoze every time I send an e-
mail.

I am running debian slink 2.0.38 with Exim version 2.05 

I use my isps smtp server to send mail, but I pick up e-mail from 
various pop-3 servers.  I have got fetchmail working fine, so that 
external e-mail is sent to local users ok.  However, when the local 
user sends a mail to be dealt with by my isp's server, depending on 
the options I configure in eximconf, the to and reply to fields are 
either user_id@localhost or user_id@the_server's_domain_name 
where user_id is different to the login name for my server.  

I need these to be configure these so that the from and reply to 
fields are :  
user_id_at_this_pop3_server@pop3_server's_domain_name.

I would like a default so that I can simply have a properly working e-
mail system independent of what mua is used, that is 
customisable for different users of this machine so that they can 
basically forge their own headers.

Thanks in anticipation.