This issue will only affect you if you have multiple Exchange 2007 servers in your network. Microsoft have the release notes for Exchange 2007 SP3 here. In that they highlight that you should upgrade any Internet facing Client Access server first – which I did for one of my clients. I then upgraded the other server in their main office to SP3… each of the clients server has the CA, MBX and HUB roles on it. What we found was that OWA now fails for any users with mailboxes on the remote Exchange 2007 servers because they are not at SP3 level. You get the following error message.
"OWA is not currently available for the user mailbox that you are trying to access. If the problem continues, contact technical support for your organisation and tell them the following: The Microsoft Exchange Client Access server that is proxying the OWA requests is running an older version of Microsoft Exchange than the Client Access Server in the mailbox Active Directory site."
Mircosofts’ guidance on the issue is that you should upgrade your CA servers first, HUB servers second and then your Edge and lastly your Mailbox servers. They provide NO guidance on if you have multiple roles on each server… I can tell you from experience – you need to upgrade ALL of them right away or else you will have things like OWA not working at all… bummer. I’ve now killed OWA for 450 users without warning… you can bet the clients IT manager is not happy with me even though I read all the proper documentation… it will be a late night tonight for sure and I just hope it will go well.
Microsoft fail once more to realise that this is a massive task for clients and they fail to provide clear guidance on the issue of multi server roles/deployments.