HELP: I am confused the use of defaulthost and envnoathost

[Uong, Hoang D]

Hi,
        I am a qmail newbie. I am confused about the use of
defaulthost and envnoathost files. It seems that I only need one
of them.
        If I send mail to 'username'.
        The qmail will fill in username@defaulthost 
and it also fill in username@envnoathost at the same time.
        Please help me to straight things out.

Thanks,

Hoang