With the Purge Messages function you can delete messages from peoples mailboxes which match specific criteria. This function can easily be used to filter out spam or other unwanted mail from your system. With Unread and Received you can delete messages that have not been read or have just been in a users mailbox for a specific period of time. The Subject, From, To and Body are all searchable for text strings. The strings you enter are not case-sensitive.
With Mailbox you can specify which user Mailbox to search in. By default it searches in All boxes. You can specify more then one criteria for your search. For example, you can search for messages that are in the Mailbox 'Trash' and have the string 'XXX' in the Subject or messages that are in the Mailbox 'Trash' and have been Unread or Received more then 2 weeks ago.