[Exim] From header of Local Delivery Mails

Hi,

I'm quite new to exim(or MTA), I use smart_host to deliver
mails to outside world, all my outgoing mails has
From: isp-acct@???
even the mail is destined to local account

How do I config exim.conf to let local mails have
From: local-acct@localhost
headers?

I guess this problem can be due to order of when to
lsearch /etc/email-addresses,
but I don't how to correct it

--
ZHENG, YOU-ZHOUNG