SharePoint 2016- Send E-mail from JavaScript using REST API

Step 1: Add Script Editor on SharePoint Page, Copy and paste below scripts.

<script type="text/javascript" src="https://ajax.aspnetcdn.com/ajax/jQuery/jquery-3.3.1.min.js"></script>

    <script type="text/javascript">

        //SUBJECT OF THE EMAIL

        //var subject = "SUBJECT OF THE MAIL";

        //CONTENT OF THE MAIL - CAN BE HTML OR PLAIN TEXT.

       // var mailContent = "<h3>Some Heading for the mail</h3><p>Content</p><div>Content</div>";

        //AN ARRAY HAVING THE RECIPIENT DETAILS.

        //THE USERNAME/EMAIL-ID SHOULD BE OF A VALID SHAREPOINT USER.

        //EXTERNAL USERS OR EXTERNAL EMAIL IDS ARE NOT SUPPORTED

       // var toList = ["DOMAIN\\USERNAME", "USER1-EMAIL-ID@DOMAIN.COM"]

             

        function processSendEmails() {

            var toList = [$("#txtUserName").val(), $("#txtRecipients").val()]

            var body = $("#txtBody").val();

            var subject = $("#txtSubject").val();

            var mailContent = "<h3>Some Heading for the mail</h3><p>" + body + "</p>";

            // Call sendEmail function      

            sendMail(toList, subject, mailContent).done(function (response) {

                alert("Mail Sent.");

            }).fail(function () {

                alert("Error while sending mail.");

            });

        }

        //Send-Email

        function sendMail(toList, subject, mailContent) {

        var restUrl = _spPageContextInfo.webAbsoluteUrl + "/_api/SP.Utilities.Utility.SendEmail",

        restHeaders = {

            "Accept": "application/json;odata=verbose",

            "X-RequestDigest": $("#__REQUESTDIGEST").val(),

            "Content-Type": "application/json;odata=verbose"

        },

        mailObject = {

            'properties': {

                '__metadata': {

                    'type': 'SP.Utilities.EmailProperties'

                },

                'To': {

                    'results': toList

                },

                'Subject': subject,

                'Body': mailContent,

                "AdditionalHeaders":

                    {

                        "__metadata":

                           { "type": "Collection(SP.KeyValue)" },

                        "results":

                        [

                            {

                                "__metadata": {

                                    "type": 'SP.KeyValue'

                                },

                                "Key": "content-type",

                                "Value": 'text/html',

                                "ValueType": "Edm.String"

                            }

                        ]

                    }

            }

        };

        return $.ajax({

            contentType: "application/json",

            url: restUrl,

            type: "POST",

            data: JSON.stringify(mailObject),

            headers: restHeaders

        });

    }

    </script>

    <table>

        <tr>

            <td>User Name(with Domain) for ex : Exdoamin\JaisonA</td>

            <td>

                <input type="text" name="txtUserName" id="txtUserName" value="" /></td>

        </tr>

        <tr>

            <td>Email Id</td>

            <td>

                <input type="text" name="txtRecipients" id="txtRecipients" value="" />

            </td>

        </tr>

        <tr>

            <td>Subject :

            </td>

            <td>

                <input type="text" name="txtSubject" id="txtSubject" value="test mail from rest APi" />

            </td>

        </tr>

        <tr>

            <td>Body :

            </td>

            <td>

                <input type="text" name="txtBody" id="txtBody" value="Testing123" />

            </td>

        </tr>

        <tr>

            <td>&nbsp;</td>

            <td>

                <input id="Button1" onclick="processSendEmails()" type="button" value="SendMail" /></td>

        </tr>

    </table>