Deleting mail from an entire inbox (purging) can be done in a few ways on Zimbra:

zmmailbox -z -m [email protected] emptyFolder /Inbox

or

zmmailbox -a admin -p password -m [email protected] emptyFolder /Inbox

or

zmmailbox
mbox> adminAuthenticate -u https://server.domain.com:7071 [email protected] password
mbox> selectMailbox [email protected]
mbox [email protected]> emptyFolder /Inbox