The remote host is missing an update to squirrelmail announced via advisory DSA 1290-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201290-1

It was discovered that the webmail package Squirrelmail performs insufficient sanitising inside the HTML filter, which allows the injection of arbitrary web script code during the display of HTML email messages. For the oldstable distribution (sarge) this problem has been fixed in version 1.4.4-11. For the stable distribution (etch) this problem has been fixed in version 1.4.9a-2. For the unstable distribution (sid) this problem has been fixed in version 1.4.10a-1. We recommend that you upgrade your squirrelmail package.