[BCC32 Error] Unit6.cpp(36): E2451 Undefined symbol 'NMPOP1'

//---------------------------------------------------------------------------
 
#include <vcl.h>
#pragma hdrstop
 
#include "Unit6.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm6 *Form6;
//---------------------------------------------------------------------------
__fastcall TForm6::TForm6(TComponent* Owner)
    : TForm(Owner)
{
}
//---------------------------------------------------------------------------
void __fastcall TForm6::Button1Click(TObject *Sender)
{
Memo1->Lines->Clear();
 IdSMTP1->Host=Edit1->Text;
 IdSMTP1->UserId=Edit2->Text;
 IdSMTP1->Password=Edit3->Text;
 IdSMTP1->Connect();
 NMPOP1->Host=Edit1->Text;
 NMPOP1->UserID=Edit2->Text;
 NMPOP1->Password=Edit3->Text;
 NMPOP1->Connect();
}
//---------------------------------------------------------------------------
void __fastcall TForm6::ComboBox1Change(TObject *Sender)
{
AnsiString subj;
 
 int tt=ComboBox1->ItemIndex+1;
 Application->ProcessMessages();
 NMPOP1->GetSummary(tt);
 subj = NMPOP1->Summary->Subject;
 Memo1->Lines->Clear();
 Memo1->Lines->Add(subj);
 NMPOP1->GetMailMessage(tt);
 TMailMessage *mess=NMPOP31->MailMessage;
 TStringList *s=mess->Body;
 Memo1->Lines->AddStrings(s);
 }
//---------------------------------------------------------------------------
void __fastcall TForm6::Button2Click(TObject *Sender)
{
IdSMTP1->Disconnect();
NMPOP31->Disconnect();
Memo1->Lines->Clear();
Memo1->Lines->Add("Соединение завершено!");
}
//---------------------------------------------------------------------------
void __fastcall TForm6::Button3Click(TObject *Sender)
{
IdMessage1->Subject=Edit5->Text;
IdMessage1->From->Address=Edit2->Text;
IdMessage1->Body->Text=Memo2->Text;
IdMessage1->Recipients->EMailAddresses=Edit4->Text; //Получатель
IdSMTP1->Send(IdMessage1);
}
//---------------------------------------------------------------------------
void __fastcall TForm6::IdSNMP1Connected(TObject *Sender)
{
Memo1->Lines->Add("Соединение!");
 int MC=NMPOP31->MailCount;
 Memo1->Lines->Add("Писем: "+IntToStr(MC));
 AnsiString fr;
 if (MC)
 {
  for (int t=1; t<=MC; t++)
  {
   Application->ProcessMessages();
   NMPOP31->GetSummary(t);
   fr = NMPOP31->Summary->From;
   ComboBox1->Items->Add(fr);
  }
 }
}
//---------------------------------------------------------------------------