The PHP manual page at:

http://www.php.net/manual/ref.imap.php3

Says to "copy" the c-client.a file into some directory in your link path.

This is just WRONG.  It doesn't work.

The page should be fixed to correct say that you need to intall the
library into some directory in your normal link path under the name:

libc-client4.a

Also, it appears that if you are on a FreeBSD 3.x system, after installing
that (static) library, it is also necessary to check to see if you already had
a *dynamic* version of this library on your system (specifically in your
/usr/local/lib directory) and if you have such a thing there already then
you MUST delete it or else the second configure step for Apache will
crash and burn in a most excruciatingly confusing and unhelpful way
that makes it all but impossible to tell what went wrong.