React Native
Mailgun Send Email using MIME

Send an email using MIME. This allows for the Chilkat email object to be used to construct the email. Then it can be sent using Mailgun.
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import { Email, Http, HttpRequest, HttpResponse, JsonObject, StringBuilder } from '@chilkat/react-native'

async function chilkatExample() {
  // This example assumes the Chilkat API to have been previously unlocked.
  // See Global Unlock Sample for sample code.

  // We're going to create an email that contains an .zip attachment,
  // and also both plain-text and HTML alternative bodies.
  // The HTML body will include an image.

  const email = new Email();

  // Adding attachments, HTML/plain-text bodies, etc can be done
  // in any order:

  // Add an attachment
  let contentType: string;
  try {
    contentType = email.addFileAttachment('qa_data/hamlet.zip');
  } catch {
    console.log(email.lastErrorText);
    return;
  }

  // Add some headers:
  email.subject = 'This is a complex email';
  // Please change this email address before testing.
  email.addTo('Joe Example', 'joe@example.com');
  email.from = 'Your Name <mailgun@YOUR_DOMAIN_NAME>';

  // Add a plain-text body:
  email.addPlainTextAlternativeBody('This is the plain-text body');

  // Add an image that will be embedded in the HTML body.
  try {
    email.addRelatedFile2('qa_data/jpg/starfish.jpg', 'starfish.jpg');
  } catch {
    console.log(email.lastErrorText);
    return;
  }

  // Add an HTML body:
  const html = '<html><body><b>This is the HTML body</b><br><img src="starfish.jpg"></body></html>';

  email.addHtmlAlternativeBody(html);

  // ------------------------------------------------------------------------
  // Send the above email using Mailgun

  const http = new Http();

  // Implements the following CURL command:

  http.login = 'api';
  http.password = 'sending_api_key';  // Replace with your actual sending API key.

  const req = new HttpRequest();
  req.httpVerb = 'POST';
  req.path = '/v3/YOUR_DOMAIN_NAME/messages.mime';
  req.contentType = 'multipart/form-data';

  req.addParam('from', 'Your Name <mailgun@YOUR_DOMAIN_NAME>');
  req.addParam('to', 'Joe Example <joe@example.com>');
  req.addStringForUpload2('message', 'message.eml', email.getMime(), 'utf-8', 'application/octet-stream');

  const resp = new HttpResponse();
  try {
    await http.httpSReqAsync('api.mailgun.net', 443, true, req, resp);
  } catch {
    console.log(http.lastErrorText);
    return;
  }

  const sbResponseBody = new StringBuilder();
  resp.getBodySb(sbResponseBody);
  const jResp = new JsonObject();
  jResp.loadSb(sbResponseBody);
  jResp.emitCompact = false;

  console.log('Response Body:');
  console.log(jResp.emit());

  const respStatusCode = resp.statusCode;
  console.log(`Response Status Code = ${respStatusCode}`);
  if (respStatusCode >= 400) {
    console.log('Response Header:');
    console.log(resp.header);
    console.log('Failed.');
    return;
  }

  // Sample JSON response:
  // (Sample code for parsing the JSON response is shown below)

  // {
  //   "id": "<20210429234809.1.2D550E1C94D3D98F@sandbox0e542e4c577f4bbb98c8bf6b6bca727b.mailgun.org>",
  //   "message": "Queued. Thank you."
  // }

  // Sample code for parsing the JSON response...
  // Use the following online tool to generate parsing code from sample JSON:
  // Generate Parsing Code from JSON

  const id = jResp.stringOf('id');
  const message = jResp.stringOf('message');
}