Amazons Cloud guys have been busy recently. Their new service Simple Email Service (or SES) has gone into beta and seems like a winner for people who spend a lot of money on mail-shot services and would like to take some control. Assuming you have already signed up for AWS and generated a new access key pair, you should download the new AWS .Net SDK here.
You need to sign up to the service by optionally entering a VAT number associated with your business. Next you need to enter your telephone number and submit, almost immediately you will receive an automated phone call that lets you enter a 4-digit verification code that is displayed one you actually submit your phone number. All fairly painless and quick.
As the service is in Beta you cannot just email anyone using the service right now. You must verify each "from" email and each "to", "cc", or "bcc" email address. But the AWS SES FAQ located here: http://aws.amazon.com/ses/faqs/ seems to indicate that this will change.