User A's mailbox deleted and create again. have same smtp address. Can send email , but when other user send email to him, cannot receive. The server will genretate the message. not exist. I ask other user delete the cache and send again , it works but if they reply the old mail , this issue still happen. Can solve it or not? Thanks

Don't reply to the old mail, it will be using the values/parameters set in the email header. Outlook has a nasty habit of using the internal (X400) addresses and not SMTP addresses when it thinks it knows about a recipient (which now no longer exists).

But It is very difficult to ask all the user dont reply. Any method to handle or work around it?

AFAIK for users internal to your Exchange organisation there is no workaround, anyone outside your Exchange organisation will be OK, as far as Exchange/Outlook are aware the mailbox is a new mailbox - but when replying Outlook will try to send to the old mailbox.

Hi Have a look at this article, it will provide you with the details about legacyexchangedn http://www.msexchange.org/tutorials/Understanding-LegacyExchangeDN.htmlJonas Andersson MCTS: Microsoft Exchange Server 2007/2010 | MCITP: EMA 2007/2010 | MCSE/MCSA Blog: http://www.testlabs.se/blog