Every exchange admin would have come across a user complaining that the new staff is not present in the address book and hence he/she can’t email the new member of staff. There are number of ways of solving this and I am sure you are all aware of it. Few solutions are to flip Outlook to online mode, download the new set of OAB files after getting the server to update it, getting the user to use OWA as a work around etc.
One solution which is of particular interest is to get Outlook to use the online Global address list while working in cached mode itself. This does mean that the network traffic between the client and server will be more and there will be much more frequent lookup request against global catalog servers. For smaller companies, they can easily turn this feature on, whereas larger companies will need to analyze the impact it has on the network, especially if they have remote locations connecting to the backend infrastructure.
All it takes is a registry edit on the client machines to configure Outlook to use the global address list. Depending on the Outlook version, edit the registry as stated below. It should be noted that mobile users should be avoided from this registry edit as they won’t have an address book otherwise (while working offline)!
Setting the value to zero prevents OAB download and forces Outlook to use the global address list. If the “Cached Mode” key doesn’t exist, create it.
Note If .oab files were previously downloaded and associated with an Outlook profile, this setting will not have the correct effect. To use this setting, you must set the registry value, remove any .oab files from the local computer and then synchronize.
Check the KB article for more info.