The Footer Object contains two properties html and text.
The html contents are used as a signature to be added to HTML content and text property is added respectively to text message contents.
footer An Object containing two properties one for html message part and one for text part.
|html||String (partial HTML)||The html content of footer|
If footer object is present this property must not be null
|text||String||The text content of the footer.|
If present should be pure UTF8 text