Daily Archives: January 3, 2006

Generating the Offline Address Book in Outlook 2003

Steve had been playing with his Offline Address book on the Exchange Server and had run into some problems with OAB generation and performance.  He’d been trying to compress the OAB when hardly anyone else was in the office and the load on the server was light.  He asked me how often the maintenance process in Exchange 2003 runs and creates the Address List entry and whether it was possible to force ithis event more frequently apart from restarting the Information store service.
There’s a really good article on how the OAB works on the TechNet site, and Dave has also written an interesting blog entry on how it works deep down….  There’s also a good KB article  841273 Administering the Offline Address Book in Outlook 2003  talks about how and when the OAB is generated.  The default setting on the Exchange computer is to generate an Offline Address Book differential file every morning at 04:00.  So if you make a change in Active Directory and want it to reach the client computer OAB, the following events must occur:

The change must be picked up by the Exchange computer that generates the Offline Address Book files. This can take several hours. At worst, it can take 24 hours. This variable will be referred to as “x.”
The Outlook clients must download the Offline Address Book updates every 24 hours. This update can take several hours. At worst, it can take 24 hours. This variable will be referred to as “y.”
The update reaches the client machines x+y hours later, and the worst delay is 48 hrs. It would be rare for a client to ever experience the complete 48-hour delay.

So to force this to happen more frequently, although its not recommended due to performance issues, here’s what you have to do…
If you want to increase the frequency of your updates, make sure your Offline Address Book is reasonably small. A good size is in the range of 1 MB to 25 MB, uncompressed.
To customize the generation of these files on the server, follow these steps:
1. In Exchange System Manager (ESM), expand the “Recipients” container.
2. Click “Offline Address Lists”.
3. Right-click the offline address list that you specified for your
   mailbox store, and then click “Properties”.
4. Click “Customize”.
5. Customize the times that you want the Offline Address Book files to
   be generated on your server.

So why is it a bad idea to do this?

Generating the Offline Address Book files on the Exchange computer on a more frequent basis may cause performance problems on the server. You can see the performance impact in the following aspects:
– The server has to generate the Offline Address Book more frequently.
  It might take hours to complete, depending on the size of Active
– For each update, Outlook must make a copy of the Offline Address Book
  in the local computer and apply the incremental changes that are
  fetched from the server. If the Offline Address Book on the local
  computer is 150 MB, Outlook would have to create a copy of that much
  data with each update.
– Outlook has a “throttling” mechanism that slows down the Offline
  Address Book update when user activity is detected. Depending on the
  size of the Offline Address Book, the update can take anywhere from one
  hour to eight hours if there is continuous user activity.

So I think that patience would be a virtue here.  Wait, and let Outlook and Exchange talk to each other when they feel like it, and don’t force them to do stuff outside of their normal schedule, otherwise they” sulk and cause you aggravation…!