Java
Mailgun Send Send HTML Email with Attachments and HTML Images

Sends an HTML email with images and attachments.
Chilkat Java Downloads

Java
import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    boolean success = false;

    // This example assumes the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    CkHttp http = new CkHttp();

    http.put_Login("api");
    http.put_Password("sending_api_key");    //  Replace with your actual sending API key.

    CkHttpRequest req = new CkHttpRequest();
    req.put_HttpVerb("POST");
    req.put_Path("/v3/YOUR_DOMAIN_NAME/messages");
    req.put_ContentType("multipart/form-data");

    // Change YOUR_DOMAIN_NAME to something like "mg.your-domain.com".
    req.AddParam("from","Your Name <mailgun@YOUR_DOMAIN_NAME>");
    req.AddParam("to","Joe Example <joe@example.com>");
    req.AddParam("subject","Hello Joe Example");
    req.AddParam("html","<html><body><b>This is the HTML body</b><br><img src=\"cid:cidStarfish.jpg\"></body></html>");

    // An a attachd file
    CkBinData bd = new CkBinData();
    success = bd.LoadFile("qa_data/hamlet.zip");
    if (success == false) {
        System.out.println("Failed to load file attachment.");
        return;
        }

    req.AddBdForUpload("attachment","hamlet.zip",bd,"application/zip");

    // add an image as CID
    success = bd.LoadFile("qa_data/jpg/starfish.jpg");
    if (success == false) {
        System.out.println("Failed to load HTML image.");
        return;
        }

    req.AddBdForUpload("inline","cidStarfish.jpg",bd,"image/jpeg");

    CkHttpResponse resp = new CkHttpResponse();
    success = http.HttpSReq("api.mailgun.net",443,true,req,resp);
    if (success == false) {
        System.out.println(http.lastErrorText());
        return;
        }

    CkStringBuilder sbResponseBody = new CkStringBuilder();
    resp.GetBodySb(sbResponseBody);
    CkJsonObject jResp = new CkJsonObject();
    jResp.LoadSb(sbResponseBody);
    jResp.put_EmitCompact(false);

    System.out.println("Response Body:");
    System.out.println(jResp.emit());

    int respStatusCode = resp.get_StatusCode();
    System.out.println("Response Status Code = " + respStatusCode);
    if (respStatusCode >= 400) {
        System.out.println("Response Header:");
        System.out.println(resp.header());
        System.out.println("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

    String id = jResp.stringOf("id");
    String message = jResp.stringOf("message");
  }
}