This extension requires the c-client library to be installed. Grab the latest version from » ftp://ftp.cac.washington.edu/imap/ and compile it.
It's important that you do not copy the IMAP source files directly into the system include directory as there may be conflicts. Instead, create a new directory inside the system include directory, such as /usr/local/imap-2000b/ (location and name depend on your setup and IMAP version), and inside this new directory create additional directories named lib/ and include/. From the c-client directory from your IMAP source tree, copy all the *.h files into include/ and all the *.c files into lib/. Additionally when you compiled IMAP, a file named c-client.a was created. Also put this in the lib/ directory but rename it as libc-client.a.
To build the c-client library with SSL or/and Kerberos support read the docs supplied with the package.
Note: In Mandrake Linux, the IMAP library (libc-client.a) is compiled without Kerberos support. A separate version with SSL (client-PHP4.a) is installed. The library must be recompiled in order to add Kerberos support.