Last month I wrote a bit about MailTips and Group Metrics processing that happens on Exchange 2010 mailbox servers. Now for some deeper follow-up.
First, E.J. Dyksen has a good post on general MailTips troubleshooting on the Exchange team blog. Go read it. (Don’t worry; I’ll wait for you to come back.)
Back already? Great. Now let’s get to it.
Group Metrics creation is on by default; it’s controlled by the organizational GroupMetricsGenerationEnabled setting. Every mailbox server that generates an OAB will also generate Group Metric data for the entire organization. Other mailbox servers will not generate any GM data, unless and until you enable them to do so.
Clients ask the CAS for Group Metric data. A given CAS server will assemble a list of Group Metrics servers, then use AD sites and site link definitions to find the "best" server for getting a copy of the Group Metrics data. The list contains servers that generate OABs for that CAS, plus mailbox servers that are explicitly enabled for Group Metrics generation. (Note that this means that CAS servers that don’t host any OABs also won’t host any Group Metrics data.)
When does all this happen? By default, Group Metric generation happens at midnight, plus or minus three hours. You can change that time using the GroupMetricsGenerationTime parameter, in which case the +/- 3-hour offset doesn’t apply. Also, after you change the time, you’ll notice that the next Group Metrics generation follows the old schedule, then the new schedule kicks in.
There’s no way to force regeneration from the UI, although you can stop and restart the Microsoft Exchange Service Host service on any server to force an update. However, updating the Group Metrics data won’t force the CAS servers to pull the new update; for that, you have to restart the Microsoft Exchange File Distribution service.