With this Zimlet installed you can enable automated replies based on a filter from within your Zimbra Web Mail.
While you could always configure Zimbra filters to send automated replies over CLI using:
/opt/zimbra/bin/zmmailbox -z -m email@example.com afrl "Filter_name" active any address "to,cc" all is "firstname.lastname@example.org" reply "Auto reply message" stop
This feature was not available to the end user in the Web Interface. This Zimlet adds a button in Preferences -> Filters -> Create Filter to add this functionality. https://github.com/Zimbra-Community/reply-by-filter