SendMail with nonblocking call

procedure MakeInvoiceClick(Sender: TObject)
begin
  if MakeInvoice(SelectedParcelList) then
    UpDateParcels(SelectedParcelList)
  else
    ShowMessage('Make invoice failed');
end;

function MakeInvoice(ASelectedParcelList: TParcelList): Boolean;
var
  oParcel: TParcel;
begin
  for oParcel in ASelectedParcelList do
  begin
    if oParcel.Electronic then
      Result := MakeEInvoice(oParcel)
    else if oParcel.MailByPDF then
      Result := MakePDFInvoice(oParcel);
  end;
end;

function MakePDFInvoice(AParcel: TParcel): Boolean
var
  oPDF: string;
begin
  oPDF := MakePDF(AParcel);
  Result := Mail.SendWait(UserData, oPDF);
end;

function TMail.SendWait(AUserData: TUSerData; const APDF: string): Boolean;
begin
  if GetSetting.UseSendGrid then
    Result := SendMailWithGrid(AUserData, APDF)       // <-- Blocking
  else if GetSetting.UseOutLook then
    Result := SendMailWithOutLook(AUserData, APDF)    // <-- None blocking
  else if GetSetting.UseSMTP then
    Result := SendMailWithSMTP(AUserData, APDF);      // <-- Blocking
end

function TMail.SendWaitWithOutLook(AUserData: TUSerData; const APDF: string): Boolean;
begin
  InitAuthentication;
  Connect;
end;

// Event called after successful authentication and Connect
procedure TMail.Connected(Sender: TObject);
begin
  ConfigureEmail;
  SendEmailMessage(UserData, Attachement);
end;

// Event called after successful send an email
procedure TMail.MessageSent(Sender: TObject; ARequestResult: TMailResult);
begin

end;