Just create a script that reads a text file for email addresses and displaynames.. It should be pretty easy with a for loop..
Here is a simple for loop that creates a user (with no display name or anything)
for i in `cat userlist`
do zmprov ca $i PASSWORD
echo "Hi and welcome to Zimbra!" | mail -s "Welcome" $i
done
If you want to make it more complicated with display names, etc.. you will need to man awk |