You will have to authenticate to the server.

use Mail::Sender;
my $sender = new Mail::Sender {smtp => 'the.mail.server.com'};
die "Error: $Mail::Sender::Error\n" unless ref $sender;
print join(', ', $sender->QueryAuthProtocols()),"\n";
[download]

will tell you what protocols are supported by the mail server. And

use Mail::Sender;
my $sender = new Mail::Sender {
  smtp => 'the.mail.server.com',
  auth => 'NTLM',
  authid => 'username',
  authpwd => 'password',
};
[download]

will log you in. I'm sure some other modules do support a few authentication protocols as well. Mail::Sender currently supports PLAIN, LOGIN, CRAM-MD5 and NTLM.

HTH, Jenda