SharePoint 2013 REST Send Email and Limitations

In order to send email from SharePoint Hosted App using REST, use the below code snippet.

var sendEmail = function (from, to, cc1, cc2, body, subject) {             
                var baseUrl = _spPageContextInfo.webServerRelativeUrl;
                var urlTemplate = baseUrl + "/_api/SP.Utilities.Utility.SendEmail";
                return getFormDigest().then(function (digest) {
                    $.ajax({
                        contentType: 'application/json',
                        url: urlTemplate,
                        type: "POST",
                        data: JSON.stringify({
                            'properties': {
                                '__metadata': { 'type': 'SP.Utilities.EmailProperties' },
                                'From': from,
                                'To': { 'results': [to, cc1, cc2] },
                                'Body': body,
                                'Subject': subject
                            }
                        }
                      ),
                        headers: {
                            "Accept": "application/json;odata=verbose",
                            "content-type": "application/json;odata=verbose",
                            "X-RequestDigest": $("#__REQUESTDIGEST").val()
                         
                        },
                        success: function (data) {
                            console.log("An email was sent.");
                        },
                        error: function (args) {
                            console.log("We had a problem and an email was not sent.");
                        }
                    });
                });
            };

However there are some limitations:

1. The To user must be a valid SharePoint user, cannot be a external user. For security reasons, it doesn't allow sending email to external users.

2. The user who is logging and executing this code should have manage web permissions.