The remote host is missing an update to exim announced via advisory DSA 635-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%20635-1

Philip Hazel announced a buffer overflow in the host_aton function in exim, the default mail-tranport-agent in Debian, which can lead to the execution of arbitrary code via an illegal IPv6 address. For the stable distribution (woody) this problem has been fixed in version 3.35-1woody4. For the unstable distribution (sid) this problem has been fixed in version 3.36-13 of exim and 4.34-10 of exim4. We recommend that you upgrade your exim and exim4 packages.