Referenced CVEs: 
CVE-2006-2659
Description: 
=========================================================== Ubuntu Security Notice USN-294-1 June 09, 2006 courier vulnerability CVE-2006-2659 =========================================================== A security issue affects the following Ubuntu releases: Ubuntu 5.04 Ubuntu 5.10 Ubuntu 6.06 LTS This advisory also applies to the corresponding versions of Kubuntu, Edubuntu, and Xubuntu. The problem can be corrected by upgrading your system to the following package versions: Ubuntu 5.04: courier-mta 0.47-3ubuntu1.5 Ubuntu 5.10: courier-mta 0.47-3ubuntu7.2 Ubuntu 6.06 LTS: courier-mta 0.47-13ubuntu5.1 In general, a standard system upgrade is sufficient to effect the necessary changes. Details follow: A Denial of Service vulnerability has been found in the function for encoding email addresses. Addresses containing a '=' before the '@' character caused the Courier to hang in an endless loop, rendering the service unusable.