[Abhey]

How to remove Email Address with .net suffix. Via AD PowerShell, Exchange Management Shell or Quest Shell.

[Adan]

An AD property or an actual Exchange email address domain? (Where the domain is *.net)

If it’s the 2nd one, why would you need a CSV? you can simply spool through your entire list of users and use this PS script.

foreach($i in Get-Mailbox -ResultSize Unlimited) {
　 $i.EmailAddresses |
　　　 ?{$_.AddressString -like '*@yourdomain.net'} | %{
　　　　　 Set-Mailbox $i -EmailAddresses @{remove=$_}
　　　 }
}

This will remove entries that has *@yourdomain.net from all mailboxes while leaving all other email addresses intact, perfect for situations where a certain OU had two domain suffixes and one was decommissioned.