This is what I use to set-up my DirectAdmin boxes with Exim, SpamAssassin, SpamFighter, BlockCracking and dkim.
cd /usr/local/directadmin/custombuild ./build set clamav yes ./build set exim yes ./build set eximconf yes ./build set eximconf_release 4.4 ./build set blockcracking yes ./build set easy_spam_fighter yes ./build set spamassassin yes ./build set sa_update daily ./build update ./build exim ./build clamav ./build spamassassin ./build exim_conf wget -O /etc/exim.dkim.conf http://files.directadmin.com/services/exim.dkim.conf service exim restart
After that you can use the file /etc/virtual/domainips to set the interface IP for exim:
*:1.2.3.4
