I noticed that the daily mail report doesn't report on attachment blocking statistics. Here's a script to get statistics for attachment block by the MTA. It could easily be extended to email in CSV format.

Code:
#!/bin/bash
#This script counts how many of each attachment extension were blocked by the MTA,
#If no messages for that extension were blocked they are omitted from the count
#created by james[dot]barnett[at]noc[dot]com

clear
cd /home/zimbra
zmprov gcf zimbraMtaBlockedExtension | cut -d: -f2>temp.txt #echo blocked attachment extensions to temp file
total=0;

echo "Number of Messages blocked by the MTA due to Attachments with banned Extensions"
echo
echo -e "Number \t | \t Extension"
for i in $(cat temp.txt); #reads the list into $i
do
        count=$(grep -c "unacceptable extension \"$i\"" /var/log/zimbra.log) #counts the number of occurences in the log of $i
        if [ "$count" -gt "1" ] #checks to see if count is greater than 1 if not then don't print report that extension
                then echo -e "$count \t | \t $i"
        fi
        if [ "$count" = "1" ] #checks to see if count is 1 (for grammatically correct output)
                then echo -e "$count \t | \t $i"
        fi
        let total+="$count" #adds the value of count to the total
done
tput smso;
echo -e "$total \t | \t total"
tput rmso;
echo
rm -f temp.txt #removes temp file