Hi,
I can't believe that even Exchange would be unable to do a retry - there are plenty of situations where a server might return a temporary 45x error.
The error isn't easy to reproduce. It seems that some conditions are necessary. It might be a race condition.
Exchange never managed it to 100% comply with the existing RFCs. That hasn't changed at all. And it still looks like Microsoft doesn't handle bugs seriously if only a small to average userbase is affected. This bug has only made it up to the second level support of Microsoft.
-- Martin