Export mail after the migration to pst between 15-11-13 and 21-11-13 (to get this command to work we had to set date into US format)
New-MailboxExportRequest -ContentFilter {(Received -lt '11/21/2013') -and (Received -gt '11/15/2013') -or (Sent -lt '11/21/2013') -and (Sent -ge '11/15/2013')} -Mailbox <username> –FilePath “\\Server01\e$\Exports\<username>.pst”

Delete content from the mailbox
search-mailbox -identity <identity> -deletecontent

Import email from the new pst (change the folderpath as per where the pst is kept)
Dir \\server01\foldername\*.pst | %{ New-MailboxImportRequest -Name SmallImport -BatchName Recovered -largeitemlimit 50 -Mailbox $_.BaseName -FilePath $_.FullName}