External bound messages stuck in queue

We have a Exchange 2007 and 2010 CASHUB co-existing.  Right now on the 2007 CASHUB, I'm seeing a "451 5.7.3 Cannot achieve Exchange Server authentication."  Attempted failover to alternate host, but that did not succeed.  Either there are no alternate hosts, or delivery failed to all alternate hosts.

The 2010 is our main outbound server, I know it's some sort of authentication issues with the receive connectors but not sure how to proceed.

Please help!
Who is Participating?
Simon Butler (Sembee)ConsultantCommented:
Have you changed the connectors on either server from their default setting? Locked them down in any way, such as Ip address restriction.
The Default Receive connector is usually used for inter-server connectivity, with Exchange Server authentication type enabled.

randy915Author Commented:
To clarify, we have mail stuck on the 2007 box to external addresses.
randy915Author Commented:
I fixed the issue by removing the Default receive connector on my 2010 and recreating it from scratch.

As a reference for others, an out of the box Default receive connector looks like this:

FQDN = computername.domain.com
Local IP address to receive mail = NIC IP on port 25
Receive mail from IP address = to
Authentication: TLS, Basic, Offer Basic after TLS, Exchange Server, Integrated Win Auth
Permission Groups:  Exchange users
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