Marketing emails are normally delivered to a large number of recipients, and must be handled carefully to avoid overloading external email systems and/or getting trapped in spam filters. This process requires central management and is resource intensive. Therefore, when you send a marketing email blast, you messages are first loaded from your Dynamics Marketing server to our bulk messaging server, which resolves any dynamic content and then manages the send. The bulk messaging server also tracks how contacts respond and interact with your messages, and returns performance data back to your Dynamics Marketing instance. Once information has been sent to your site, it is purged from the bulk email server.
For more information about how emails are sent through this system, and how the send status is presented in Dynamics Marketing, see Track email send status.