Deleting more than 10k messages at a time

Hello,

I am trying to figure out how to delete a large amount of messages from an office 365 mailbox using powershell. I am using the below command to delete messages, but it is only cleaning up 10k a time. I've tried the New-MailboxSearch cmdlet and it has not worked correctly. Please, assist.

Search-Mailbox-Identityapp_support-SearchQuery'(Received:09/20/2012..03/28/2013)'-deletecontent

Basically as noted above I need to be able to mass delete more than 10k messages at a time...this SHOULD not be this difficult.

Thanks,

Jonathan