The remote host is missing an update to cyrus-imapd-2.2 announced via advisory DSA 2242-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%202242-1

It was discovered that the STARTTLS implementation of the Cyrus IMAP server does not properly restrict I/O buffering, which allows man-in-the-middle attackers to insert commands into encrypted IMAP, LMTP, NNTP and POP3 sessions by sending a cleartext command that is processed after TLS is in place. For the oldstable distribution (lenny), this problem has been fixed in version 2.2.13-14+lenny4. For the stable distribution (squeeze), this problem has been fixed in version 2.2.13-19+squeeze1. For the unstable distribution (sid), this problem has been fixed in version 2.2.13p1-11 for cyrus-imapd-2.2 and in version 2.4.7-1 for cyrus-imapd-2.4. We recommend that you upgrade your cyrus-imapd-2.2 packages.