[SLUG] Probably a trivial sendmail question

[Laurie Savage <savage99@xxxxxxxxxxx>]

I'm using Postfix out of the Mandrake 8.1 box

On our domestic machine are 4 local users each with their own bigpond.com 
mail account.

What do I type and where so the headers read bigponduserx@xxxxxxxxxxx instead 
of localuserx@xxxxxxxxxxx?

Fetchmail has its nice "bigponduserx there localuserx here" syntax. Is there 
a comparable Postfix synatx in one of its files?

Laurie Savage