What is Free/Busy?
Users' availability information is stored in Exchange in a hidden system public folder. This information is used by Outlook and OWA to tell other users if they are free or busy (hence, the term Free/Busy information). Normally this information is displayed as color-coded blocked out areas in a user's calendar, as show above. If users have extended rights, they can right-click another user's blocked out time to view the subject of the busy time.
The Free/Busy information is posted as a single message that contains data for the entire Free/Busy duration. The default to publish is 2 month's worth of information, configurable in Outlook Options or via Group Policy. Every time the Free Busy information is updated, the message is overwritten.
Publishing Free/Busy Information
The way Free/Busy information is published to Exchange depends on the method used to update the user's calendar. The Outlook client is usually responsible for generating Free/Busy information. Outlook will read the calendar and generate Free/Busy every 15 minutes by default if the information has been changed. This schedule can be changed in Outlook options or via Group Policy. Outlook also republishes the Free/Busy information whenever Outlook is shut down.
So what happens when the user updates their calendar using Outlook Web Access (OWA) or some other non-MAPI client? In this case, Free/Busy information is updated by a background process called MSExchangeFBPublish (MadFB). This process runs under the System Attendant mailbox and updates Free/Busy every 5 minutes for OWA, OMA, and Entourage clients. When a change is made to the calendar, a Free/Busy message is submitted to the System Attendant mailbox on the mailbox server for the user. The MadFB process polls this mailbox and picks up that there has been a change. MadFB then publishes the user's full Free/Busy message to the Free/Busy folder overwriting the existing message.
Replicating Free/Busy Information
The short answer is don't do it. The only reason to replicate Free/Busy information is when you frequently have users accessing Free Busy information of users in another site, and those sites are separated by a slow or lossy network link. Replicating Free/Busy information introduces inherent latency and causes inaccuracy in the Free/Busy information. Users in one site may see information from a site that has not replicated yet.
Where is Free/Busy Information Stored?
As mentioned earlier, Free/Busy information is stored in a system public folder. You can view all the Free/Busy information in the org by opening the following URL in a web browser: "http(s)://ServerName
Here, you will see a folder under SCHEDULE+ FREE BUSY for each Administrative Group in the format, "EX:/o=
Free/Busy message placement is based on the user's legacyExchangeDN attribute in AD. For example, if my legacyExchangeDN is /o=CompanyABC/ou=Paris/cn=Recipients/cn=jsguillet", my Free Busy information will be stored in the "USER-/CN=RECIPIENTS/CN=jsguillet" message in the "/EX:/o=CompanyABC/ou=Paris" folder.
You are unable to view the contents of the message, but you can delete it. Doing so will remove all Free Busy information from Exchange until it is republished using one of the methods explained above. If Free/Busy information is not available to other users, they will see black and white hash marks across your calendar and Outlook will say that Free/Busy information is not available for this user.
How to Republish Free/Busy Information
On occasion Free/Busy information may not be published correctly in Exchange. There are many reasons that this can occur. Examples include errors in Public Folder replication (if Free Busy is being replicated, another reason to not do this), network errors, and incorrect shutdown of Outlook or Windows.
So how do you republish Free/Busy information? The easiest way to do this for individual users is to have them run Outlook with the /CleanFreeBusy switch:
- Close Outlook
- Click Start, Run, enter "start outlook /cleanfreebusy" and click OK
- Outlook will start, generate the Free/Busy information from the Outlook calendar and republish it to Exchange within 5 minutes. It will overwrite any existing Free/Busy message or publish a new one if it doesn't exist.
While this is easy to do for one or two users, it isn't a good solution for all users in the enterprise since it requires user intervention.
Microsoft KB article 294282 details how to use Updatefb.exe to regenerate Free/Busy information from the calendar information contained in each user's mailbox. You run this utility under the context of a user or service account that has full mailbox access to the affected users. It reads a comma delimited file containing the alias and home mailbox server of each user (i.e., alias, mailbox1) and logs in as that user using Collaboration Data Objects (CDO). It then creates a single appointment for the user for today at 11:00pm. This marks the Free/Busy information as "dirty". It then logs off the MAPI connection, causing the Free/Busy information to republish to Exchange. Note that Updatefb will be unable to open disabled user's or hidden mailboxes, so be sure to exclude them from the CSV input file.
Updatefb.exe is an unsupported utility written by Microsoft and is only available through Microsoft Product Support Services. There are two versions of the utility, Updatefb.exe is the GUI version and CPPCDO.exe is a command line version. I have used it in several environments with no issues.
What About Exchange 2007?
Exchange 2007 uses an entirely new and different way to manage Free/Busy information, so the above does not apply in a pure Exchange 2007/Outlook 2007 environment. When using Exchange 2007 with Outlook 2007 Free/Busy information will no longer come from a Public Folder, but will instead use the Microsoft Exchange 2007 Availability Service. This web service will provide a direct look at the user's Free/Busy information without the need of a client publishing any data. Outlook 2007 and Exchange 2007 can still use (and will still have) the Free/Busy public folder for backwards compatibility with older Outlook clients.