problem when Sending message to groups in exchange 2000

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Dear All ;
Can you help me to solve this problem in exchange 2000 Messaging systems .

Environment description :
Active directory with tow domains , Acorp (root)and Bcorp
Exchange Server is joined to Bcorp domain.
All domain controllers are in the same site .
FSMO and global catalog servers are distributed between domain controllers.
Exchange 2000 Version 6.0 (Build 6249.4: Service Pack 3) Enterprise Edition installed on Win2K Advanced Server with SP4.

Problem description:
When I send message to a local group , some times this message doesn’t reach the recipients ( members of this group) , and the message appears in sent items folder .

When I track the message I notice the following

Event Time event

8/7/2005 12:05 PM SMTP: Message Submitted From Store
8/7/2005 12:05 PM SMTP: Message Submitted to advanced Queuing .
8/7/2005 12:05 PM SMTP: Started Message Submition to Advanced Queue.
8/7/2005 12:05 PM SMTP: Message Submitted to categorizer .



Note : the message does not delivered locally to multiple recipients

Any One Can help please
Thank in advance