If you resend a Simple Mail Transfer Protocol (SMTP) mail by using Outlook (a Messaging Application Programming Interface [MAPI] client), the message ID in the SMTP mail that you resent may be the same as the message ID in the original SMTP mail.
NOTE: This behavior is different than the behavior in Exchange Server version 5.5. In Exchange Server 5.5, if you use Outlook to resend an SMTP mail, Exchange Server 5.5 uses a unique message ID for the resent message.
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