Your network contains an Active Directory domain. The domain contains one site.
You have an Exchange Server 2010 Service Pack 1 (SP1) organization that contains two
Client Access servers, two Hub Transport servers, and three Mailbox servers. The mailbox
servers are members of a database availability group (DAG) named DAG1.
Users report that they fail to receive email messages from the Internet.
You review the message tracking logs and discover that the organization failed to receive
any email messages from the Internet during the past hour.
You need to identify what is preventing the Hub Transport servers from receiving email
messages.
What should you run from the Exchange Management Shell?

A.
Get-MailboxDatabaseCopyStatus

B.
Test-AvailabilityService

C.
checkdatabaseredundancy.psl

D.
Test-MapiConnectivity

E.
Get-MailboxDatabase

F.
Test-SMTPConnectivity

G.
Retry-Queue

H.
Test-ReplicationHealth

I.
Test-WebServicesConnectivity

J.
Test-SenderID
K.
Get-SenderIDConfig
L.
Test-MailFlow
M.
Test-OutlookWebServices
N.
Test-SystemHealth

Explanation:

http://technet.microsoft.com/en-us/library/ff849710.aspx