The remote host is missing an update to postfix-policyd announced via advisory DSA 1361-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201361-1

It was discovered that postfix-policyd, an anti-spam plugin for postfix, didn't correctly bounds-test incoming SMTP commands potentially allowing the remote exploitation of arbitrary code. For the stable distribution (etch), this problem has been fixed in version 1.80-2.1etch1. For the old stable distribution (sarge), this package was not present. For the unstable distribution (sid), this problem was fixed in version 1.80-2.2. We recommend that you upgrade your postfix-policyd package.