I've just renamed courier-0.49.0.ebuild and it installed and is working in 3 different servers without a problem. Reproducible: Always Steps to Reproduce:
There is 0.50.1 ebuild in portage, could you give it a whirl and report here if it works for you?
Mass re-assign, seems like mail-mta/courier needs a maintainer.
Reporter, see comment #1 and reopen then.