var urlTemplate = appweburl + "/_api/SP.Utilities.Utility.SendEmail";
 $.ajax({
    contentType: 'application/json',
    url: urlTemplate,
    type: "POST",
    data: JSON.stringify({
        'properties': {
            '__metadata': { 'type': 'SP.Utilities.EmailProperties' },
            'From': 'steve.curran@somewhere.com',
            'To': { 'results': ['smc750@somewhere.com'] },
                'Body': 'Hello',
                'Subject':'remember'
            }
    }
  ),
    headers: {
        "Accept": "application/json;odata=verbose",
        "content-type": "application/json;odata=verbose",
        "X-RequestDigest": $("#__REQUESTDIGEST").val()
    },
    success: function (data) {
        var result = data.d.results;
        var i = result.length;
    },
    error: function (err) {
        alert(JSON.stringify(err));
    }