You could introduce your company's SMTP server and some creative /etc/hosts resolving on your SUNbox?
Our sendmail is configured w/the following options:
DMyourCOMPANY.com (masquerade company email address)
DSmail.COMPANY.com (this is the default route for all outgoing mail, which will be resolved in hosts file locally)
now in /etc/hosts, resolve mailCOMPANY.com by associating it w/your company's SMTP server (It will also include an alais for your exchange server domain).
192.x.x.x EXCHANGEdefaultDOMAIN.net mailCOMPANY.com
I believe it is this EXCHANGEdefaultDOMAIN.net entry that allows exchange to receive incoming mail. You will notice that it is recognized when performing a sendmail test (sendmail -v
exchangeUSER@COMPANY.com).
no DNS, everything is resolved locally.