Export-Mailbox is no longer supported in Exchange 2010 sp1, in stead there is New-MailboxExportRequest but the problem is that “-DeleteContents” is not supported with mailbox export.
In order to be able to search and delete emails from multiple Exchange 2010 mailboxes one has to have the following roles assigned.
New-ManagementRoleAssignment -Role "Support Diagnostics" –User username
New- ManagementRoleAssignment -Role "Mailbox Import Export" -User username
above will ensure that a user has proper permissions to perform this command.
In order to find and delete a certain email from one mailbox you can perform the following command
Search-Mailbox -Identity username -SearchQuery 'subject:"Email Subject that you want to search for"' –DeleteContent
this can be run for all mailboxes on a server as well
Get-Mailbox –Server “*servername*” –ResultSize unlimited | Search-Mailbox -SearchQuery 'subject:"Email Subject that you want to search for"' –DeleteContent