imap_include="-I${IMAP_TK_DIR}/include"
imap_ldflags="-I${IMAP_TK_DIR}/lib"
imap_libs="-lc-client"
CPPFLAGS="${CPPFLAGS} ${imap_include}"
LIBS="${LIBS} ${imap_libs} ${imap_ldflags}"
<AC_LINK_IFELSE check goes here>

Kevin: Is this what you meant for me to do in the case when an IMAP directory is specified and
there does not appear to be a source installation in that directory? I think this is what
you were saying to do, but I wanted to double-check before I started testing.