When an Outlook user composes and sends a message using either Rich Text Format or HTML Format, Outlook automagically generates a file, winmail.dat, and attaches it to the end of the email. The winmail.dat contains the rich text body and original attachments. To parse winmail.dat (TNEF stream) file, we should use ParseTNEF method.
The following code demonstrates how to parse MAPI winmail.dat in email.
// The following example codes demonstrate parsing winmail.dat - TNEF stream
// To get full sample projects, please download and install EAGetMail on your machine.
// To run it correctly, please change email server, user, password, folder, file name value to yours
Unit Unit1; 
Interface 
Uses 
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, 
  Dialogs, StdCtrls, EAGetMailObjLib_TLB; 
Type 
  TForm1 = Class(TForm) 
    Button1: TButton; 
    Procedure Button1Click(Sender: TObject); 
  private 
    { Private declarations } 
  public 
    { Public declarations } 
  End; 
Const 
  MailServerPop3 = 0; 
  MailServerImap4 = 1;   CRYPT_MACHINE_KEYSET = 32; 
  CRYPT_USER_KEYSET = 4096; 
  CERT_SYSTEM_STORE_CURRENT_USER = 65536; 
  CERT_SYSTEM_STORE_LOCAL_MACHINE = 131072; 
Var 
  Form1: TForm1; 
Implementation 
{$R *.dfm} 
Procedure TForm1.ParseEmail( fileName: WideString ); 
Var 
  oMail: TMail; 
  i, UBound, x, XBound: Integer; 
  addrs, atts, tatts: OleVariant; 
  addr: IMailAddress; 
  att, tatt: IAttachment; 
  oCert: TCertificate; 
  oSignerCert: ICertificate; 
Begin 
  oMail := TMail.Create(Application); 
  oMail.LicenseCode := 'TryIt'; 
  oMail.LoadFile(fileName, false); 
  ShowMessage(oMail.Headers.GetValueOfKey('Content-Type')); 
  If oMail.IsEncrypted Then 
    Try 
      // this email is encrypted, decrypt it by default user certificate
      oMail.ConnectTo(oMail.Decrypt(nil)); 
      // You can also use specified certificate like this
      // oCert := TCertificate.Create(Application);
      // oCert.LoadFromFile( 'c:\test.pfx', 'pfxpassword', CRYPT_USER_KEYSET );
      // oMail.Load(oMail.Decrypt(oCert.DefaultInterface).Content);
    Except 
      On ep: Exception Do 
      Begin 
        ShowMessage('Decrypt Error: ' + ep.Message ); 
      End; 
    End; 
  If oMail.IsSigned Then 
     Try 
      // this email is digital signed, verify signature
      oSignerCert := oMail.VerifySignature(); 
      ShowMessage( 'This email contains a valid digital signature.' ); 
      // You can add the certificate to your certificate storage like this
      // oSignerCert.AddToStore(CERT_SYSTEM_STORE_CURRENT_USER,
      // 'addressbook');
      // Then you can use send the encrypted email back to this sender.
    Except 
      On ep: Exception Do 
      Begin 
        ShowMessage('Verify signature Error: ' + ep.Message ); 
      End; 
    End; 
  // Parse email sender
  ShowMessage( 'From: ' + oMail.From.Address ); 
  // Parse email to recipients
  addrs := oMail.ToAddr; 
  UBound := VarArrayHighBound( addrs, 1 ); 
  For i := 0 To UBound Do 
  Begin 
    addr := IDispatch(VarArrayGet(addrs, i)) As IMailAddress; 
    ShowMessage( 'To: ' + addr.Address ); 
  End; 
  // Parse email cc recipients
  addrs := oMail.Cc; 
  UBound := VarArrayHighBound( addrs, 1 ); 
  For i := 0 To UBound Do 
  Begin 
    addr := IDispatch(VarArrayGet(addrs, i)) As IMailAddress; 
    ShowMessage( 'Cc: ' + addr.Address ); 
  End; 
  // Parse email subject
  ShowMessage( 'Subject: ' + oMail.Subject ); 
  // Parse email text body
  ShowMessage( 'Text body: ' + oMail.TextBody ); 
  // Parse email HTML body
  ShowMessage( 'HTML body: ' + oMail.HtmlBody ); 
  // Parse attachment
  atts := oMail.Attachments; 
  UBound := VarArrayHighBound( atts, 1 ); 
  For i := 0 To UBound Do 
  Begin 
    att := IDispatch(VarArrayGet(atts,i)) As IAttachment; 
    ShowMessage( att.Name ); 
    If LowerCase(att.Name) = 'winmail.dat' Then 
    Begin 
      // this is outlook rtf (TNEF) attachment, decode it here
      tatts := oMail.ParseTNEF(att.Content, true ); 
      XBound := VarArrayHighBound(tatts, 1 ); 
      For x:= 0 To XBound Do 
      Begin 
        tatt := IDispatch(VarArrayGet(tatts,x)) As IAttachment; 
        ShowMessage( 'winmail.dat' + tatt.Name ); 
      End; 
    End 
  End; 
End; 
Procedure TForm1.Button1Click(Sender: TObject); 
Begin 
  Try 
      ParseEmail('c:\my folder\test.eml'); 
  Except 
    On ep:Exception Do 
      ShowMessage( 'Error: ' + ep.Message ); 
  End; 
End; 
End. 
If you have any comments or questions about above example codes, please add your comments here.