"ticket": {
    "assignee": {
        "id": "testing1@test.com",
        "name": "John Doe"
    },
    "events": [
        {
            "author": {
                "id": "testing@test.com",
                "name": "testing",
                "type": "agent1"
            },
            "date": "2014-08-18T10:05:05Z",
            "is_private": false,
            "message": "Hey, I have a problem with...",
            "source": {
                "type": "agent-app-manual",
                "url": null
            },
            "type": "message"
        }
    ],

    "groups": [
        {
            "id": 0,
            "name": "All operators"
        }
    ],
    "id": "CCWWM",

    "requester": {
        "mail": "test@test.com",
        "name": "Mary Brown"
    },
    "status": "test1",
    "subject": "issue1"
}

$data = file_get_contents('php://input');
$data = json_decode($data);

$email = $data->visitor->email;

$email = $data->ticket->visitor->email;