The remote host is missing an update to the system as announced in the referenced advisory FreeBSD-SA-06:17.sendmail.asc

Upgrade your system to the appropriate stable release or security branch dated after the correction date https://secure1.securityspace.com/smysecure/catid.html?in=FreeBSD-SA-06:17.sendmail.asc

FreeBSD includes sendmail(8), a general purpose internetwork mail routing facility, as the default Mail Transfer Agent (MTA). A suitably malformed multipart MIME message can cause sendmail to exceed predefined limits on its stack usage.