Delphi DLL
Mailgun Send Send HTML Email with Attachments and HTML Images

Sends an HTML email with images and attachments.
Chilkat Delphi DLL Downloads

Delphi DLL
uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Http, HttpResponse, JsonObject, StringBuilder, BinData, HttpRequest;

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Boolean;
http: HCkHttp;
req: HCkHttpRequest;
bd: HCkBinData;
resp: HCkHttpResponse;
sbResponseBody: HCkStringBuilder;
jResp: HCkJsonObject;
respStatusCode: Integer;
id: PWideChar;
message: PWideChar;

begin
success := False;

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

http := CkHttp_Create();

CkHttp_putLogin(http,'api');
CkHttp_putPassword(http,'sending_api_key');//  Replace with your actual sending API key.

req := CkHttpRequest_Create();
CkHttpRequest_putHttpVerb(req,'POST');
CkHttpRequest_putPath(req,'/v3/YOUR_DOMAIN_NAME/messages');
CkHttpRequest_putContentType(req,'multipart/form-data');

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

// An a attachd file
bd := CkBinData_Create();
success := CkBinData_LoadFile(bd,'qa_data/hamlet.zip');
if (success = False) then
  begin
    Memo1.Lines.Add('Failed to load file attachment.');
    Exit;
  end;
CkHttpRequest_AddBdForUpload(req,'attachment','hamlet.zip',bd,'application/zip');

// add an image as CID
success := CkBinData_LoadFile(bd,'qa_data/jpg/starfish.jpg');
if (success = False) then
  begin
    Memo1.Lines.Add('Failed to load HTML image.');
    Exit;
  end;
CkHttpRequest_AddBdForUpload(req,'inline','cidStarfish.jpg',bd,'image/jpeg');

resp := CkHttpResponse_Create();
success := CkHttp_HttpSReq(http,'api.mailgun.net',443,True,req,resp);
if (success = False) then
  begin
    Memo1.Lines.Add(CkHttp__lastErrorText(http));
    Exit;
  end;

sbResponseBody := CkStringBuilder_Create();
CkHttpResponse_GetBodySb(resp,sbResponseBody);
jResp := CkJsonObject_Create();
CkJsonObject_LoadSb(jResp,sbResponseBody);
CkJsonObject_putEmitCompact(jResp,False);

Memo1.Lines.Add('Response Body:');
Memo1.Lines.Add(CkJsonObject__emit(jResp));

respStatusCode := CkHttpResponse_getStatusCode(resp);
Memo1.Lines.Add('Response Status Code = ' + IntToStr(respStatusCode));
if (respStatusCode >= 400) then
  begin
    Memo1.Lines.Add('Response Header:');
    Memo1.Lines.Add(CkHttpResponse__header(resp));
    Memo1.Lines.Add('Failed.');
    Exit;
  end;

// 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

id := CkJsonObject__stringOf(jResp,'id');
message := CkJsonObject__stringOf(jResp,'message');

CkHttp_Dispose(http);
CkHttpRequest_Dispose(req);
CkBinData_Dispose(bd);
CkHttpResponse_Dispose(resp);
CkStringBuilder_Dispose(sbResponseBody);
CkJsonObject_Dispose(jResp);

end;