You can forward any mail you wish without having a mailbox, all you need is to create a contact. You will save your CALs if you do it this way. You can also accept mail and forward them automatically to the vendor. Let's say your mail server is authoritative for @SMTP25.org .Now you want to forward all e-mails sent to vendor@Smtp25.org to the outside E-mail address Vendor@Vendor.org. You do not want to create an account, due to security concerns, or you want to save your CALS.
Simply create a contact called Vendor@Smtp25.org and add second SMTP address to the same contact Vendor@Vendor.org . When mail send to the SMTP address Vendor@Smtp25.org your Exchange server will accept the mail, since the SMTP address Vendor@Smtp25.org is valid, owned by an contact object, than your server will see the TargetAddress attribute has an outside SMTP address (in this example Vendor@Vendor.com and forward the mail out to the internet for delivers to this SMTP address.
If you never knew the attribute called "TargetAddress" you
would think this can only be achieved by enabling forward option on the mail box by pointing to a contact
It is simple and clean