Delphi DLL
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.
Chilkat Delphi DLL Downloads

Download Chilkat for Delphi DLL
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, Email, StringBuilder, JsonObject, HttpRequest;

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Boolean;
email: HCkEmail;
contentType: PWideChar;
html: PWideChar;
http: HCkHttp;
req: HCkHttpRequest;
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.

// 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.

email := CkEmail_Create();

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

// Add an attachment
contentType := CkEmail__addFileAttachment(email,'qa_data/hamlet.zip');
if (CkEmail_getLastMethodSuccess(email) = False) then
  begin
    Memo1.Lines.Add(CkEmail__lastErrorText(email));
    Exit;
  end;

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

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

// Add an image that will be embedded in the HTML body.
success := CkEmail_AddRelatedFile2(email,'qa_data/jpg/starfish.jpg','starfish.jpg');
if (success = False) then
  begin
    Memo1.Lines.Add(CkEmail__lastErrorText(email));
    Exit;
  end;

// Add an HTML body:

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

CkEmail_AddHtmlAlternativeBody(email,html);

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

http := CkHttp_Create();

// Implements the following CURL command:

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.mime');
CkHttpRequest_putContentType(req,'multipart/form-data');

CkHttpRequest_AddParam(req,'from','Your Name <mailgun@YOUR_DOMAIN_NAME>');
CkHttpRequest_AddParam(req,'to','Joe Example <joe@example.com>');
CkHttpRequest_AddStringForUpload2(req,'message','message.eml',CkEmail__getMime(email),'utf-8','application/octet-stream');

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');

CkEmail_Dispose(email);
CkHttp_Dispose(http);
CkHttpRequest_Dispose(req);
CkHttpResponse_Dispose(resp);
CkStringBuilder_Dispose(sbResponseBody);
CkJsonObject_Dispose(jResp);

end;