Karmic Koala open for development

Packages in the "universe" component of Ubuntu (like courier) are usually provided more or less as-is from Debian. Most of them do not have a separate maintainer in Ubuntu, and the version which is included in an Ubuntu release is generally a matter of timing relative to Debian. Most of them do not receive updates once they are released (including security updates). In opting to use those packages, a system administrator is taking on an additional responsibility for maintenance beyond what the Ubuntu community can provide.

If you care about courier, and want to make sure that it's solid in each Ubuntu release, by all means dive in and help to maintain it. Otherwise, if you find that a version from Debian meets your needs better, you are welcome to use it instead.