Importing a PST fails when using New-MailboxImportRequest

I have a requirement to import some PST files into different mailboxes in Exchange.  This is easy to do using the New-MailboxImportRequest PowerShell cmdlet however when it fails it isn’t easy to see why.  Fortunately, we can get more information by using the Get-MailboxImportRequestStatistics cmdlet

Firstly, get the name of the request from the list by using Get-MailboxImportRequest:

Get-MailboxImportRequest | Get-MailboxImportRequestStatistics

Next get the identity of the request that failed:

$Request = Get-MailboxImportRequest -Name Mailboximport
$ID = $Request.Identity

And now run the following to get a report:

Get-MailboxImportRequest -Identity $ID | Get-MailboxImportRequestStatistics -IncludeReport | Format-List

Look at the Message and Report sections of the output for clues as to why the import failed.