Sendmail question

[Rick Lim]

I know that this isn't quite the correct forum for this question, but I
thought I would ask anyways.

I am running sendmail on one server for 2 different domains.
For company A the mail gets sent and received correctly
For company B the mail gets received correctly.

But for company B when the mail is send directly from the server box (logged
on as company_b_user) the from address shows correctly i.e.
company_b_user at companyb.com.

When that user sends mail from his outlook at home and relays thru the
server the from address shows up as company_b_user at companya.com 

I am using the virtusertable, genericstable and the generics-domains.

Anyone know how to rewrite the from address correctly, the from email
address in MS outlook shows company_b_user at companyb.com 
Any help would be appreciated.
TIA