In my vacations i had trouble with disk size and ended with thousands of emails in my inbox sent by zimbra cron processes, trying to delete them with user interface was a pain, with CLI command line interface was very easy and fast.

# Step 1.- Create temporary file with the delete command for the id of all the emails to remove, filtering the subject begining with "Disk / at ":

zimbra@server:~$ zmmailbox -z -m search -l 1000 Subject:"Disk / at "| awk '/Disk \/ at/ {print "deleteItem " $2 }' > /tmp/deletes-user

# note the -l argument with the maximun of items is required to override the 25 default, it can't exceed 1000, and if you have more messages. you must iterate many times steps 1 and 2.

# 2.- Execute the command file massively against the mailbox:

zimbra@server:~$ zmmailbox -z -m < /tmp/deletes-user

The base information was this post:
- Script to delete old calendar items:
- wiki of zmmailbox: Zmmailbox - Zimbra :: Wiki