Exchange UM Messages are not Delivered to Mailboxes

When MSExchange Unified Messaging Event IDs 1423 and 1446 are being logged on the Exchange Unified Messaging server(s), this indicates that there are issues with the UM server delivering messages to the Hub/Transport server(s).  

A couple of the common culprits I have seen cause this are:

1) Proper Antivirus exclusions not specified on the Exchange servers

For Exchange 2007 File-Level Antivirus Exclusions:

http://technet.microsoft.com/en-us/library/bb332342(v=exchg.80).aspx 

For Exchange 2010 File-Level Antivirus Exclusions:

http://technet.microsoft.com/en-us/library/bb332342.aspx 

2) Overlapping subnets defined on the Exchange 2010 Receive Connectors

When configuring new Receive Connectors on the Hub/Transport server(s), be careful not to include networks and/or subnets which include other Exchange servers.  The only Receive Connector which should include Exchange server IP addresses is the "Default" Receive Connector.  To put it another way, it is not a good idea to setup a new Receive Connector with blanket subnets which cover your entire server range(s).  Although it may seem like a good idea, it can lead to headaches with email transport from other Exchange servers.


When Exchange 2010 determines the Receive Connector on which it will receive a message, it uses the more specifically defined or restrictive connector.  For example:


Receive Connector A

Receive Connector B

Mail is relayed from another Exchange server with the IP of 10.20.0.1.  If both of the above are configured as Receive Connectors, then Receive Connector A will be used to receive the messages.  You must also be sure that Receive Connector A has the proper Authentication and Permission Groups applied in order to accept mail from other Exchange servers.  This means that "Exchange Server authentication" (Authentication Tab) and Exchange servers (Permission Groups Tab) should be enabled on Receive Connector A.


-Phil