We'll use exim 4.76 for the example, so if you need a new/older version, just replace all instances of that version with the version you want (assuming we have it on our server).
wget http://files.directadmin.com/services/da_exim-4.76-1.src.rpm
rpmbuild --rebuild --force da_exim-4.76-1.src.rpm
rpm -Uvh /usr/src/redhat/RPMS/i386/da_exim-4.76-1.i386.rpm
/etc/init.d/exim restart
DirectAdmin