The problem can be corrected by adding a valid X.400 address to the sender's mailbox properties on the Email Addresses tab in the Microsoft Exchange Administrator program.
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A similar condition might also result if the recipient of the message does not have a valid X.400 address.
This condition does not affect message delivery between mailboxes on the same Microsoft Exchange Server because the Information Store submits the message to the mailbox directly. It will only occur when the message is being routed to another Microsoft Exchange Site via one of the Site Connectors, when the message is going between two Microsoft Exchange Servers in the same Site, or when a message is addressed to go out a connector to a foreign system, in other words, using the Microsoft Exchange Internet Mail Connector.
The X.400 addresses in Microsoft Exchange should never be deleted because Microsoft Exchange is a native X.400 messaging system
Maxwell