The remote host is missing an update to icedove announced via advisory DSA 2317-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%202317-1

CVE-2011-2372 Mariusz Mlynski discovered that websites could open a download dialog - which has open as the default action -, while a user presses the ENTER key. CVE-2011-2995 Benjamin Smedberg, Bob Clary and Jesse Ruderman discovered crashes in the rendering engine, which could lead to the execution of arbitrary code. CVE-2011-2998 Mark Kaplan discovered an integer underflow in the javascript engine, which could lead to the execution of arbitrary code. CVE-2011-2999 Boris Zbarsky discovered that incorrect handling of the window.location object could lead to bypasses of the same-origin policy. CVE-2011-3000 Ian Graham discovered that multiple Location headers might lead to CRLF injection. As indicated in the Lenny (oldstable) release notes, security support for the Icedove packages in the oldstable needed to be stopped before the end of the regular Lenny security maintenance life cycle. You are strongly encouraged to upgrade to stable or switch to a different mail client. For the stable distribution (squeeze), this problem has been fixed in version 3.0.11-1+squeeze5. For the unstable distribution (sid), this problem has been fixed in version 3.1.15-1. We recommend that you upgrade your icedove packages.