Fixed! Thanks everybody.
I only add a sub "over" and comment the sub "quit" in sendMail :

sub over {
  $self = @_;
  $self->{SMTP}->quit;
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Then i add the sub in end of my a.pl

  ...
  use MySMTP;
  $mail = new MySMTP();
  my @lists = $mail->get_list();
  
  for my $addr (@list) {
      $mail->sendMail($addr,"how are you");    
  }
  $mail->over();  ## Add here
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