Hi Rich,
Here are two ways of solving this.
a. use an account with minimal rights on exchange server, but that do have the 'send as' rights.
b. Allow anonymous send on your exchange server smtp connector ONLY from the ip address of the crm server. The advantage is that you can then setup the outgoing connector to use anonymou ssmtp. The disavantage is that you need to allow anonymous relay from that CRM server ip.
Alex Fagundes -
www.PowerObjects.com