How many messages are send with System.Net.Mail.SmtpClient.Send() if multiple recipients are specified?

I have some code which uses System.Net.Mail.SmtpClient.Send to send data from a piece of software I maintain. We're charged on the amount of data we send so it's crucial that we identify the most cost effective way to distribute the information.

If I spec开发者_如何学编程ify multiple recipients, am I right in thinking the software would be transmitting one email per recipient? i.e. if each email was 1MB and I had three recipients, I'd be sending 3MB?

Usually when you send a mail with multiple recipients, your client sends one email to your provider and this is responsible to send one message to every recipient...
If you want to be sure, use WireShark to monitor SMTP port you use and check the traffic amount.

EDITED:
My previous answer was true if you have an external provider; situation can be different if you have an internal mail server in your company: in this case your server is responsible to send this email and, according to its configuration (using a smarthost, etc...), it could send a single email to an external provider or send multiple emails one for each recipient.
In this case you must check what happens on SMTP port of your server.