The remote host is missing an update to sendmail announced via advisory DSA 1155-2. It turned out that the sendmail binary depends on libsasl2 (>= 2.1.19.dfsg1) which is neither available in the stable nor in the the security archive. This version is scheduled for the inclusion in the next update of the stable release, though. You'll have to download the referenced file for your architecture from below and install it with dpkg -i. As an alternative, temporarily adding the following line to /etc/apt/sources.list will mitigate the problem as well: deb http://ftp.debian.de/debian stable-proposed-updates main Here is the original security advisory for completeness: Frank Sheiness discovered that a MIME conversion routine in sendmail, a powerful, efficient, and scalable mail transport agent, could be tricked by a specially crafted mail to perform an endless recursion.
For the stable distribution (sarge) this problem has been fixed in version 8.13.4-3sarge2. For the unstable distribution (sid) this problem has been fixed in version 8.13.7-1. We recommend that you upgrade your sendmail package. https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201155-2