Are there any recommendations or suggestions how to set up and configure the calendar synchronization correctly, in order to avoid most common issues?
Recommendations or suggestions how to set up and configure the calendar synchronization are made by Professional Services, consultants and Solution Architects, after thoroughly analyzing the environment and the needs.
Below are some thoughts, which might help to make the correct decision.
Calendar Synchronization in Migration Manager always offers two options:
For regular users mailboxes it offers one-way synchronization
For resource mailboxes it offers two-way synchronization.
Most common confusion is to assume that a two-way synchronization is better or that it is needed for absolutely all mailboxes.
In reality a two-way synchronization is not needed at all, and if enabled it is jeopardizing the migration and introducing some risk. The biggest advantage of Migration Manager is that all the parts of the tool never modify anything in the source environment. Should something unpredictable happen one can always resynchronize or re-migrate and recover from the damage. But once two-way calendar synchronization is established the agent will access and modify the data in the source and if something happens in the target then the agent will synchronize this change back to the source, and there will be no easy way to repair the damage.
It is always being assumed that a two-way calendar synchronization is absolutely needed for resource mailboxes, in order for booking of resources to work properly between both organizations.
However this is incorrect. One-way synchronization is fully sufficient in this situation. If target users will book a resource this request will be redirected to the source (by using the Quest redirection) and the item will be created in the source mailbox, then the Calendar Synchronization will take care of the rest and will copy the item to the target environment. This is a simple non-technical explanation.
But: One-way synchronization is sufficient only for room mailboxes, this means that the source and target should be at least Exch 2007 or Exch 2010. This will not work for resource mailboxes, which have Direct Booking enabled. Having Direct Booking is the only option in Exch 2003, but can be also configured/allowed in 2007 and 2010.
One-way calendar sync will work properly for resource mailboxes only if you disable the Direct booking agent in Exchange and reboot (or restart the services).
Explanation: When Direct Booking is enabled/allowed then a user in the target books directly to the target calendar and the meeting is never synced/redirected back to the source.
This means that when relying on the one-way calendar synchronization one needs to verify and configure the Exchange properly, so the source and target mailboxes auto-accept meeting requests, when they have been forwarded via the SMTP connector (more info can be found when reading about ProcessExternalMeetingMessages).
In the past the calendar synchronization was working slow in some environments, this was caused by different environmental factors. For example the agents were working slowly on cluster servers (known issue) or one single agent had to process many mailboxes, or the agent was updating the Free-Busy information, and the list goes on. But all those issues were typical only for the older versions of the tool and for older Exchange environments, with older Exchange server and older Outlook versions.
Today QMM offers some advanced features like multiple Calendar Synchronization Agents, this allows admisn to split the load and to use multiple agents more efficiently, so there is almost no delay when synchronizing the data from source to the target.
A two-way calendar synchronization was needed sometimes in the past, but is almost never needed when using QMM 8.8. Avoiding two-way calendar synchronization is always a good idea, because this will minimize any risk and will never introduce any possible damage to the source environment.
And careful planning allows utilizing the one-way calendar synchronization very efficiently.
Important: Using one-way synchronization for resource mailboxes assumes that they are the last to be switch. It is a good idea to use dedicated agents for such mailboxes, and also to use dedicated synchronization agents for mail and calendar sync, in order to minimize the sync delta from source to target for switched users.