Send an email from Drupal interface?
An easy way could be using Rules and a custom content type. 

The content type should have a title which can be used as the email title, a body for email body, and a field to hold email address(es) (or perhaps a reference field to site users or roles).

Then configure a new rule. Select new content event, add a filter to restrict to defined content type, then as an action select send email. Map the proper inputs and you are done.