Hi,
depending on the Exchange configuration, the messages could have been delivered to the Postmaster / Administrator, bounced to the original senders, or both.
Please use the message tracking module from Exchange to verify what happened with the messages:
Exchange 2000 and 2003:
http://support.microsoft.com/kb/262162Exchange 2007:
http://msdn.microsoft.com/en-us/library/bb124375%28v=exchg.80%29.aspxRegards,
Eclarsys Support