Sending received draft messages

A colleague has sent me some draft emails as attachments to a message.
When I open the attachments to revise the emails before sending, the send button is greyed out.
How can I send them?

To send these messages, you first need to save these items to your own Drafts folder.

Drag & drop works best to achieve this easily; select the attachment in the Reading Pane and click and hold the mouse button to drop it in the Drafts folder.

When you now open the item from the Drafts folder, the Send button is active so you can send the message.