Webmail Horde Deleting
Configure your Webmail (Horde Groupware) to delete messages from Inbox on regular basis
3.) Check the box for "Move deleted message to Trash.." Choose Trash from dropdown, Purge to Daily (or as you like) & then click Save.
You have successfully configured your Webmail to empty your Trash on daily basis. Remember that you cannot retrieve any mails from server once removed from Trash.