Shadow redundancy was left turned on as default.
2x EX2010 Hub Transport with RGC to Exchange 2003 cluster in site1. Both HT’s can send over the RGC.
2x EX2010 Hub Transport with RGC to Exchange 2003 cluster in site2. Both HT’s can send over the RGC.
EX2010 RU4, EX2003 SP2
1 of the HT’s in Site2 was turned off to apply a hotfix.
During this time E-mails from Exchange 2010 users in site1 which had been sent to Exchange 2003 users in both sites the day before or earlier were then received again, presumably coming from the Shadow cache on the other HT.
These messages had definitely been delivered via EX2003 so we do not understand why they had been retained in the cache (if indeed they had been).
Shadow redundancy has now been turned off