The remote host is missing an update to icedove announced via advisory DSA 1696-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201696-1

For details, please visit the referenced security advisories. For the stable distribution (etch) these problems have been fixed in version 1.5.0.13+1.5.0.15b.dfsg1+prepatch080614i-0etch1. Packages for s390 will be provided later. For the upcoming stable distribution (lenny) these problems will be fixed soon. For the unstable (sid) distribution these problems have been fixed in version 2.0.0.19-1. We recommend that you upgrade your icedove packages.