How can I delete all occurrences of a message from a Microsoft Exchange Server 2007 mail database? Is this possible through power shell ?

Yes, you can do with Export-Mailbox, export the message to pst or any mailbox and delete the source message in all mailboxes on a database. Example : get-mailbox Database DB1 | Export-Mailbox ContentKeywords "Virus message" TargetMailbox Administrator TargetFolder 'MyData' DeleteContent Reference: Exchange Server 2007 Cross Mailbox Search using Export-mailbox Export-Mailbox