The remote host is missing an update to postfix announced via advisory DSA 2233-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%202233-1

Several vulnerabilities were discovered in Postfix, a mail transfer agent. The Common Vulnerabilities and Exposures project identifies the following problems: CVE-2009-2939 The postinst script grants the postfix user write access to /var/spool/postfix/pid, which might allow local users to conduct symlink attacks that overwrite arbitrary files. CVE-2011-0411 The STARTTLS implementation does not properly restrict I/O buffering, which allows man-in-the-middle attackers to insert commands into encrypted SMTP sessions by sending a cleartext command that is processed after TLS is in place. CVE-2011-1720 A heap-based read-only buffer overflow allows malicious clients to crash the smtpd server process using a crafted SASL authentication request. For the oldstable distribution (lenny), this problem has been fixed in version 2.5.5-1.1+lenny1. For the stable distribution (squeeze), this problem has been fixed in version 2.7.1-1+squeeze1. For the unstable distribution (sid), this problem has been fixed in version 2.8.0-1. We recommend that you upgrade your postfix packages.