The remote host is missing an update to maildrop announced via advisory DSA 1981-2.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201981-2

The latest DSA for maildrop introduced two regressions. The maildrop program stopped working when invoked as a non-root user, such as with postfix. Also, the lenny version dropped a dependency on the courier-authlib package. For the stable distribution (lenny), this problem has been fixed in version 2.0.4-3+lenny3. For the oldstable distribution (etch), this problem has been fixed in version 2.0.2-11+etch2. For the testing distribution (squeeze) this problem will be fixed soon. For the unstable distribution (sid), this problem has been fixed in version 2.2.0-3.1. For reference, the original advisory text is below. Christoph Anton Mitterer discovered that maildrop, a mail delivery agent with filtering abilities, is prone to a privilege escalation issue that grants a user root group privileges. We recommend that you upgrade your maildrop packages.