The message texts used by ZipBack are simple text files. The first line defines the SUBJECT of the message, and must end with a carriage return. Everything after that is inserted into the BODY of the message, and your zip file is added at the end of the message.
To create your own messages just click the New button and edit the blank message that appears. You must save it in your ZipBack applicaion folder, though, and you should change the name as you save it. You can use any name you like as long as it has the '.txt' extension. (If you use the name New Message that is the default for all newly created messages, it will be over-written next time you click the New button!)
To edit an existing message, click the Edit button above the message window. When you close it the list of existing messages is updated. The 'Default' message is always chosen when the message window first opens. However you can freely edit the text of this message as well.