cd /usr/local/directadmin/custombuild
mkdir -p custom/ap2
cp configure/ap2/configure.apache custom/ap2/configure.apache
vi custom/ap2/configure.apache

add: –enable-expires

so it looks like this:

#!/bin/sh
"./configure" \
        "--prefix=/etc/httpd" \
        "--exec-prefix=/etc/httpd" \
        "--bindir=/usr/bin" \
        "--sbindir=/usr/sbin" \
        "--sysconfdir=/etc/httpd/conf" \
        "--enable-so" \
        "--enable-dav" \
        "--enable-dav-fs" \
        "--enable-dav-lock" \
        "--enable-suexec" \
        "--enable-deflate" \
        "--enable-unique-id" \
        "--with-suexec-caller=apache" \
        "--with-suexec-docroot=/" \
        "--with-suexec-gidmin=100" \
        "--with-suexec-logfile=/var/log/httpd/suexec_log" \
        "--with-suexec-uidmin=100" \
        "--with-suexec-userdir=public_html" \
        "--with-suexec-bin=/usr/sbin/suexec" \
        "--with-included-apr" \
        "--with-pcre=/usr/local" \
        "--includedir=/usr/include/apache" \
        "--libexecdir=/usr/lib/apache" \
        "--datadir=/var/www" \
        "--localstatedir=/var" \
        "--enable-logio" \
        "--enable-ssl" \
        "--enable-rewrite" \
        "--enable-proxy" \
        "--with-ssl=/usr" \
        "--enable-headers" \
        "--enable-expires"
./build clean
./build apache
service httpd restart

you may need to recompile php after this

./build php