Sendmail masquerading

I am having a problem with my sendmail configuration I have masquerading on but when I send a mail to multiple people it masquerades my email but not the others? see the sample below:

From: name@vegena.net
Sent: Friday, July 24, 2009 9:42 AM
To: name2@atksco1.vegena.net; name3@atksco1.vegena.net; name4@atksco1.vegena.net; name5@atksco1.vegena.net
Subject: Used Inventory

in this way if someone does a reply to all names 2,3,4 and 5 bounce back as bad addresses.

how can I have it masquerade all email addresses from my domain?

Thanks,

Gary