The remote host is missing an update to mailx announced via advisory DSA 044-1.
The mail program (a simple tool to read and send email) as distributed with Debian GNU/Linux 2.2 has a buffer overflow in the input parsing code. Since mail is installed setgid mail by default this allowed local users to use it to gain access to mail group. Since the mail code was never written to be secure fixing it properly would mean a large rewrite. Instead of doing this we decided to no longer install it setgid. This means that it can no longer lock your mailbox properly on systems for which you need group mail to write to the mailspool, but it will still work for sending email. This has been fixed in mailx version 8.1.1-10.1.5. If you have suidmanager installed you can also make this manually with the following command: suidregister /usr/bin/mail root root 0755