Outlook updates the mail's body with the user's signature when the Outlook inspector window is initialized. To do that, call the method OutlookMail.getInspector().
Example code:
Outlook outlook = new Outlook();
OutlookMail mail = new OutlookMail(outlook);
// Get the mail signature:
mail.getInspector();
String mailSignature = mail.getHTMLBody();
System.out.println(mailSignature);
outlook.dispose();
Outlook outlook = new Outlook();
OutlookMail mail = new OutlookMail(outlook);
mail.setSubject("subject");
mail.setTo("test@example.com");
// Add the picture as attachment:
mail.getAttachments().add(new File("test.gif"));
// Reference the attached picture in the body:
mail.setHTMLBody("<html>This is a picture: " +
"<img src='cid:test.gif'></html>");
mail.send();
outlook.dispose();