The remote host is missing an update to exim4 announced via advisory DSA 2232-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%202232-1

It was discovered that Exim, the default mail transport agent in Debian, uses DKIM data obtain from DNS directly in a format string, potentially allowing malicious mail senders to execute arbitrary code. (CVE-2011-1764) The oldstable distribution (lenny) is not affected by this problem because it does not contain DKIM support. For the stable distribution (squeeze), this problem has been fixed in version 4.72-6+squeeze1. For the unstable distribution (sid), this problem has been fixed in version 4.75-3. We recommend that you upgrade your exim4 packages.