Property height

The height property is used inside separator blocks to configure how much whitespace it should represent, this will default to 4px.

{
    "from" : "info@example.com",
    "subject" : "Email with a dashed separator",
    "content" : {
        "blocks" : [ 
            {
                "type" : "text",
                "content" : "First paragraph"
            }, 
            {
                "type" : "separator",
                "height" : 10
            }, 
            {
                "type" : "text",
                "content" : "Second paragraph"
            } 
        ]
    }
}

For more information and more examples, please check the documentation of separator blocks.