Hello Panos Klaoudatos,
Generally for sending the newsletters we use WebServices. The control that is used is NewsletterSendingProgress which inherits form Composite control. The control requires Newsletter control panel. The statuses are defind in INewsletter - isDraft, isBeingSend etc. By default we use StartSending() whih is protected and you can use DataManager for sending.
However, if you are going to implement some logic for the backend you should create a custom webservices should be used by your custom control. If you can provider some code of your control witch some description we could see what is the easiest way for this task.
the Telerik team