subdomain delegation for email routing

[afactor]

Please let me clarify:

Management's stated desire is to reduce the load on the corporate email
server which is currently straining under the virus/spam/worm
load. Management feels strongly that email that is forwarded to the
outside customer care vendor should not place a load on the corporate
email server. Management also feels that there should not be a delay in
the delivery of said email (although arguably that delay may not be
significant).

I believe that none of this mail is ever NOT forwarded although I can't
say for certain whether the forwarding is done manually or not
(incredibly I believe the forwarding of the email to the vendor may be a
manually started batch job). The only requirement is that a copy of the
email is saved/sent/forwarded to the primary company (for DR/backup
reasons).

Having said that I can't put an alias in the company's mail server as that
doesn't meet the first requirement of eliminating delivery to the
corporate email server. And my second choice of setting up a second email
server and delegating a zone to it (e.g., care.company1.com) was nixed as
the company doesn't want to spend the capital.

BTW, correct me if I am mistaken but I need to delegate a subdomain not
because there are alot of users in the domain (actually there are just a
handful of email addresses I need to handle) but because if I create and
delegate a subdomain in DNS the mail delivered to these users will bypass
the corporate mail server and go directly to the mail server configured in
the NS server assigned to the new subdomain.

[Actually the above paragraph/question was what prompted me to send email
to baylisa: I'd like verification that what I am thinking of doing will
work as I imagine it will :)].

Unfortunately management prefers not to go this route. They do not have
any qualms about delegating a newly created subdomain to the outside
vendor just for the purpose of delivering this email. While the company is
fairly large (national, retail, 100 stores, etc.) I don't believe they
have configured any subdomains in their dns namespace.

So what about if the handful of email addresses are changed from
customer-care-east at company1.com to customer-care-east at care.company1.com and
instead of forwarding them to company1 at webvendor.com I create a  subdomain 
and assign the NS record to webvendor.com:
care.company1.com IN NS ns.webvendor.com

... Assuming they correctly setup their dns server and mail server to
accept email from care.company1.com.

--Alan