uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ExtCtrls, IdPOP3, IdBaseComponent, IdComponent, IdTCPConnection,
  IdTCPClient, IdExplicitTLSClientServerBase, IdMessageClient, IdSMTPBase,
  IdSMTP, StdCtrls, ComCtrls, Grids, IdMessage, IdIOHandler, IdCoder3to4,
  IdIOHandlerSocket, IdIOHandlerStack, IdSSL, IdSSLOpenSSL, IdSASLLogin,
  IdSASLExternal, IdUserPassProvider, IdSASL_CRAM_MD5, IdSASL_CRAM_SHA1,
  IdSASLPlain, IdSASLSKey, IdSASLOTP, IdSASLAnonymous, IdAttachment, IdGlobal,
  IdSASLUserPass, IdSASLDigest, IdText, IdCoderMIME, IdCoder,
  IdAttachmentFile, IdAttachmentMemory;


type
  TCalendarData = class
    cdHost: string; //Strato: smtp.strato.de
    cdAccount: string; //Mr. T's Mailaccount
    cdPort: integer; //Strato: 465 or 587
    cdUseTLS: integer;
    cdSSLConnection: boolean; //Strato: True
    cdTransferEmail: string; //Strato: you@youraccout.de
    cdUser: string; //Strato: you@youraccout.de
    cdPass: string; //Strato: Strato Password
    cdOrganizer: string; //Organisator
    cdAttendee: string; //Empfänger
    cdAppointmentStart: TDateTime; //Anfang Termin
    cdAppointmentEnd: TDateTime; //Ende Termin
    cdSummary: string; //Betreff
    cdLocation: string; //Ort
    cdBody: TStringList; //Body
    cdDescription: string; //Beschreibung
    cdPriority: TIdMessagePriority; //Prioriät
    constructor Create;
    destructor Destroy; override;
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

constructor TCalendarData.Create;
begin
  inherited;
  cdBody := TStringList.Create;
end;

destructor TCalendarData.Destroy;
begin
  cdBody.Free;
  inherited;
end;


procedure SendCalendarRequest(CD: TCalendarData);
var
  IdMessage: TIdMessage;
  SMTP: TIdSMTP;
  SSLHandler: TIdSSLIOHandlerSocketOpenSSL;
  IdUserPassProvider: TIdUserPassProvider;
  IdSASLCRAMMD5: TIdSASLCRAMMD5;
  IdSASLCRAMSHA1: TIdSASLCRAMSHA1;
  IdSASLPlain: TIdSASLPlain;
  IdSASLLogin: TIdSASLLogin;
  IdSASLSKey: TIdSASLSKey;
  IdSASLOTP: TIdSASLOTP;
  IdSASLAnonymous: TIdSASLAnonymous;
  IdSASLExternal: TIdSASLExternal;
  MemoryStream: TMemoryStream;
  Attachment: TIdAttachment;

begin
  MemoryStream := TMemoryStream.Create();
  IdMessage := TIdMessage.Create(nil);
  try
    with IdMessage, cd do
    begin
      AttachmentEncoding := 'mime';
      ContentTransferEncoding := 'base64';
      //ContentTransferEncoding := '7-bit';
      Encoding := meMIME;
      ContentType := 'text/html';
      Charset := 'utf-8';
      From.Name := cdAccount;
      From.Address := cdOrganizer;
      Recipients.EMailAddresses := cdAttendee;
      Priority := cdPriority;
      Body.Text := '';
      //Body.AddStrings(cd.cdBody);
      Attachment.ContentType:='text/calendar';//set the content type to text/calendar
    // Attachment := TIdAttachment.Create(IdMessage.MessageParts, cdBody.ToString);
    end; //with IdMessage, md
    SMTP := TIdSMTP.Create(nil);
    try
      if 1=1 then //CD.edSSLConnection
      begin
        SSLHandler := TIdSSLIOHandlerSocketOpenSSL.Create(SMTP);
        with SSLHandler do
        begin
          MaxLineAction := maException;
          SSLOptions.Method := sslvTLSv1;
          SSLOptions.Mode := sslmClient;
          SSLOptions.VerifyMode := [];
          SSLOptions.VerifyDepth := 0;
        end; //with SSLHandler
        SMTP.IOHandler := SSLHandler;
        SMTP.UseTLS := utUseImplicitTLS; //utUseExplicitTLS;
      end;
      if (cd.cdUser <> '') or (cd.cdPass <> '') then
      begin
        SMTP.AuthType := satSASL;
        IdUserPassProvider := TIdUserPassProvider.Create(SMTP);
        IdUserPassProvider.Username := cd.cdUser;
        IdUserPassProvider.Password:= cd.cdPass;
        IdSASLCRAMSHA1 := TIdSASLCRAMSHA1.Create(SMTP);
        IdSASLCRAMSHA1.UserPassProvider := IdUserPassProvider;
        IdSASLCRAMMD5 := TIdSASLCRAMMD5.Create(SMTP);
        IdSASLCRAMMD5.UserPassProvider := IdUserPassProvider;
        IdSASLSKey := TIdSASLSKey.Create(SMTP);
        IdSASLSKey.UserPassProvider := IdUserPassProvider;
        IdSASLOTP := TIdSASLOTP.Create(SMTP);
        IdSASLOTP.UserPassProvider := IdUserPassProvider;
        IdSASLAnonymous := TIdSASLAnonymous.Create(SMTP);
        IdSASLExternal := TIdSASLExternal.Create(SMTP);
        IdSASLLogin := TIdSASLLogin.Create(SMTP);
        IdSASLLogin.UserPassProvider := IdUserPassProvider;
        IdSASLPlain := TIdSASLPlain.Create(SMTP);
        IdSASLPlain.UserPassProvider := IdUserPassProvider;
        SMTP.SASLMechanisms.Add.SASL := IdSASLCRAMSHA1;
        SMTP.SASLMechanisms.Add.SASL := IdSASLCRAMMD5;
        SMTP.SASLMechanisms.Add.SASL := IdSASLSKey;
        SMTP.SASLMechanisms.Add.SASL := IdSASLOTP;
        SMTP.SASLMechanisms.Add.SASL := IdSASLAnonymous;
        SMTP.SASLMechanisms.Add.SASL := IdSASLExternal;
        SMTP.SASLMechanisms.Add.SASL := IdSASLLogin;
        SMTP.SASLMechanisms.Add.SASL := IdSASLPlain;
      end
      else
      begin
        SMTP.AuthType := satNone;
      end;
      SMTP.Host := cd.cdHost;
      SMTP.Port := cd.cdPort;
      SMTP.ConnectTimeout := 30000;
      SMTP.UseEHLO := True;
      SMTP.Connect;
      try
        SMTP.Send(IdMessage);
        finally
        SMTP.Disconnect;
      end; //try..finally
    finally
      SMTP.Free;
    end; //try..finally
  finally
    MemoryStream.Free;
    IdMessage.Free;
  end; //try..finally
end; //SendCalendarRequest

begin
  //Sende Besprechungseinladungen
  cd := TCalendarData.Create();
  with cd do
  begin
    cdHost := Edit3.Text;
    cdAccount := 'Auto Calendar'; //Mr. T's Mailaccount
    cdPort := StrToInt(Edit6.Text); //Strato: 465 or 587
    cdUseTLS := Combobox1.ItemIndex;
    cdSSLConnection := True; //Strato: True
    cdTransferEmail := Edit2.Text; //Strato: you@youraccout.de
    cdUser := Edit4.Text; //Strato: you@youraccout.de
    cdPass := Edit5.Text; //Strato: Strato Passwort
    cdOrganizer := 'calendar@xyz.de'; //Organisator
    cdAttendee := 'empfaenger@xyz.de'; //Empfänger
    cdAppointmentStart := Now; //Anfang Termin
    cdAppointmentEnd := Now+0.1; //Ende Termin
    cdSummary := 'Besprechung Meier (wwewe)'; //Betreff
    cdLocation := 'Büro XY'; //Ort
    cdDescription := 'Dies ist ein Text;'; //Beschreibung
    cdPriority := mpNormal; //Prioriät
    with cdBody do
    begin
      Add('BEGIN:VCALENDAR');
      Add('VERSION:1.0');
      Add('BEGIN:VEVENT');
      Add('ATTENDEE:' + cdAttendee);
      Add('ORGANIZER:MAILTO:' + cdOrganizer);
      Add('DTStart:' + FormatDateTime('YYYYMMDD', cdAppointmentStart) + 'T' + FormatDateTime('HHMMSS', cdAppointmentStart) + 'Z');
      Add('DTEnd:' + FormatDateTime('YYYYMMDD', cdAppointmentEnd) + 'T' + FormatDateTime('HHMMSS', cdAppointmentEnd) + 'Z');
      Add('LOCATION:' + cdLocation);
      Add('UID:LeanCredit.de');
      Add('SUMMARY:' + cdSummary);
      Add('DESCRIPTION:' + cdDescription);
      Add('PRIORITY:5');
      Add('END:VEVENT');
      Add('END:VCALENDAR');
    end; //cdBody
  end; //cd
  SendCalendarRequest(cd);
end.