The remote host is missing an update to postfix announced via advisory USN-1131-1.
Details:
Thomas Jarosch discovered that Postfix incorrectly handled authentication mechanisms other than PLAIN and LOGIN when the Cyrus SASL library is used. A remote attacker could use this to cause Postfix to crash, leading to a denial of service, or possibly execute arbitrary code as the postfix user.
Solution: The problem can be corrected by updating your system to the following package versions: