Custom message in Salesforce (Classic & Lightning)

You can add a custom message to your prefilled buttons. We advise you to use the message form field in the snippet. If you change the message in window.SR_SETTINGS make sure to use the backticks (`) and not a normal apostrophe ('). You can simply use 'enter' in this message. 

msg: `This is a demo message.

Kind regards,

Your name
`,  //(optional) prefill the message

You can create a custom message in your custom button by filling in the message field in the button snippet.

There are 2 options:

1. An existing custom button within a standard object

2. An existing custom button within a custom object

If you haven't made the button yet, you should first create one.

1. An existing custom button within a standard object

Setup > Build > Customize > Your object > Buttons, Links, and Actions

2. An existing custom button within a custom object

Here the objective is to find the button you want to change as well, but the path is a little bit different.

Setup > Build > Create > Objects > Your object > Buttons, Links, and Actions