Windows – Hybrid on-prem connector – Won’t validate – Backlog of emails

I believe you NEED to do the 'activation by phone' since this the new hardware will unable you to receive a new key to successfully activate. You might have missed the step where it asks you what kind of activation procedure you want to run. If that doesn't work, try running the repair again as something might have gone south, I've had that happened before.

Update
Did you replace a motherboard bought with the OEM license for your system? You might want to read this: (From http://www.michaelstevenstech.com/moving_xp.html)

Advisory: Changing a Branded OEM XP system motherboard to a non-factory replacement motherboard or moving a hard drive with OEM XP pre installed to a non-OEM system is not advised. The new OEM EULA states: The sale of XP OEM software is only allowed when accompanied with a complete computer. Defined as "We grant you a nonexclusive right to distribute an individual software license only with a fully assembled computer system. A "fully assembled computer system" means a computer system consisting of at least a central processing unit, a motherboard, a hard drive, a power supply, and a case." A non-password protected explanation can be accessed from the link below.

OEM Microsoft Windows (including XP Pro and XP Home) Licensing Changes You Need To Know About!

Two problem areas exist.

1. Non-compliance with the OEM EULA.
2. The OEM's practice of using a set of restore disks or hidden restore folders on the hard drive to satisfy Microsoft's restore requirement.

The first example can result in a denial of activation. The second means you have no media (i.e. no XP CD) to use for the repair install if it is necessary.

Generic OEM versions would seem to classify the builder of the computer as the OEM and as the OEM can determine what upgrades are allowed. See this link to confuse you even more. OEM

You should set up a receive connector operating on a non-standard port (maybe 2525) and restrict it to only accept IP addresses of servers that you know are allowed to send out. Create the connector with nothing ticked in Authentication and Anonymous users ticked for permissions groups.

After that you'll need to run the following command in PS as Exchange by default blocks anonymous relaying on any receive connector.

Get-ReceiveConnector “Receive Connector Name” | Add-ADPermission -User “NT AUTHORITY\ANONYMOUS LOGON” -ExtendedRights “Ms-Exch-SMTP-Accept-Any-Recipient”

I just tested this on my own exchange server and managed to send to both gmail and my own domain, sending from the exchange domain as well as a fake domain.

Also add the -port 2525 argument onto your PS script.