I'd like my own From lines to show "The Boss" boss@af.mil
rather than god@heaven.af.mil. 
Answer:
Add MAILHOST=af.mil, MAILUSER=boss and and MAILNAME='The Boss'
to your environment.
To override From lines supplied by your MUA, add QMAILINJECT=f to your
environment. 
All the users on this host, zippy.af.mil, are users on af.mil.
When joe sends a message to fred, the message should say 
From: joe@af.mil
To: fred@af.mil
 
without zippy anywhere.
Answer:
echo af.mil > /var/qmail/control/defaulthost
chmod 644 /var/qmail/control/defaulthost
           
Mail-Followup-To automatically?
I'd like to include
Mail-Followup-To: sos@heaven.af.mil
When I send a message to the sos@heaven.af.mil mailing list.
Answer:
Add QMAILMFTFILE=$HOME/.lists to your environment, and put
sos@heaven.af.mil into $HOME/.lists.