Latest version of courier introduces a new dependency lib courier-unicode. I therefore dropped all archs I am unable to test. If you want your arch to have courier please re-add your keyword to courier-unicode and courier-0.74.0. I think there are probably not many people running complex mailservers like courier on anything else than amd64 so you might just decide to un-cc your arch and drop courier support.
Marked ~hppa.
marked ~x86. I also took courier-0.74.1... Thanks!
courier-unicode became a dependency for courier-imap-4.16.0, thus keywords have been dropped from courier-imap-4.16.0. Please keyword >=net-libs/courier-unicode-1.1 >=net-mail/courier-imap-4.16.0
~arm added
Marked ~ppc64.
The only thing missing for alpha is courier-imap-4.16.0 -- which doesn't compile, see bug 556964.
~mips added to requested packages, as well as net-libs/courier-authlib. Compile-tested only.