Автор: http://www.swissdelphicenter.ch

{
  Here is some code I successfully used te determine
  the DEFAULT mailaccount, which is used in
  Outlook Express, to send outgoing mail via SMTP.
}

procedure TForm1.ReadRegistryDefaults;
var
  Registry: TRegistry;
  AccountStr: string;
begin
  Registry := TRegistry.Create;
  try
    Registry.RootKey := hkey_CURRENT_USER;
    if Registry.OpenKey('software\microsoft\internet account manager', False)
      then {}
    begin
      AccountStr := Registry.ReadString('default mail account');
      Registry.CloseKey;
      if (AccountStr <> '') then
        if
          Registry.OpenKey('software\microsoft\internet account manager\accounts\'
          +
          AccountStr, False) then {}
        begin
          Edit_Server.Text := Registry.ReadString('SMTP Server');
          Edit_Account.Text := Registry.ReadString('SMTP Email Address');
          Registry.CloseKey;
        end;
    end;
  finally
    Registry.Free;
  end;
end;