The remote host is missing an update to notmuch announced via advisory DSA 2416-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%202416-1

It was discovered that Notmuch, an email indexer, did not sufficiently escape Emacs MML tags. When using the Emacs interface, a user could be tricked into replying to a maliciously formatted message which could lead to files from the local machine being attached to the outgoing message. For the stable distribution (squeeze), this problem has been fixed in version 0.3.1+squeeze1. For the testing distribution (wheezy) and unstable distribution (sid), this problem has been fixed in version 0.11.1-1. We recommend that you upgrade your notmuch packages.