Interestingly, I use the "NMS" FormMail.pl, which runs SENDMAIL from the same website, and there is not a problem. I see "NMS" uses a pipe

sub newmail {
  my ($self, $scriptname, $postmaster, @recipients) = @_;

  my $command = $self->{Mailprog};
  $command .= qq{ -f "$postmaster"} if $postmaster;
  my $pipe;
  eval { local $SIG{__DIE__};
         $pipe = IO::File->new("| $command");
       };
  if ($@) {
    die $@ unless $@ =~ /Insecure directory/;
    delete $ENV{PATH};
    $pipe = IO::File->new("| $command");
  }

  die "Can't open mailprog [$command]\n" unless $pipe;
  $self->{Pipe} = $pipe;

  $self->output_trace_headers($scriptname);
}
[download]

At line 430 in the version of FormMail.pl I have

use IO::File;
[download]

.. is IO::File part of the NMS libraries, or a standard Perl one ? (I have no idea if they are called libraries)

Peter