The SMG-SP client library which is integrated with customer MTA does not detect the reset connection until it attempts to use it. When that occurs and the connection has been reset, the client returns an error to the MTA process before attempting to reconnect to the bmserver process resulting in the MTA deferring that first email message following lost connection.
This is a known issue and will be addresed in a future release by attempting to reconnect to the bmserver process before returning an error to the mail server.
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