We migrated about a year ago to a hosted Outlook 2007 environment. We have an application that sends out informational emails. Ever since we moved to the hosted email, internal recipients have not received some of these emails. Months of investigation have revealed that approximately two of every three emails from this application are getting duplicated InternalMessageIds -- the messages have the same time stamp and subject line but different size and body content.
So, how is the InternalMessageId set? What can we do, either from the application end or in Exchange, to get all the emails delivered?