As per the guidelines of the ACMA Spam Act 2003 and the Privacy Laws 2014, it is mandatory for marketing messages to clearly mention the Sender and also include an ‘Opt Out’ in every message (Reply STOP to OptOut). Heavy fines could be levied on the message sender if a complaint is made.
You can add the ‘Reply STOP to OptOut’ as a standard ending so that you don’t have to do this every time and it automatically comes up in your message. You can set-up a standard suffix here: CONTACTS > SETTINGS > Suffix
The above guidelines are only the main components of Spam Act compliance. You will find key elements of Spam Act here: SPAM ACT Key Elements