The Junk Email folder is often considered to be an Outlook 2003 feature. Indeed, Outlook 2003 includes a client side anti-spam filter that leverages this folder. It also provides the interface for enabling it and for configuring safe senders, safe recipients and blocked senders lists. Nevertheless the Junk Email folder is also available to all other Outlook versions serving as Exchange 2003 clients.
I covered many details regarding the Junk Email folder in a previous article series:
Bringing Together the Exchange Anti-SPAM Cocktail
Enabling/Disabling the Junk Email Folder
Centralizing Junk Email Folder Administration
The scope of these articles is quite broad. I suggest you to go through them since they touch this subject and other related information. However, considering how often I get questions on this topic, today I will present the information exclusively relevant to this aspect. I will also go further and delve into some points not covered by those articles.
The Exchange 2003 Intelligent Message Filter provides the option to deposit spam to the Junk Email folder. Most importantly, this functionality is not dependent in any manner on Outlook 2003.
When using earlier Outlook versions, the Junk Email folder is not present. These clients came about before Exchange 2003, when this functionality was not supported. Some are tempted to try and create it manually. Creating a folder named "Junk E-mail" does not work and Exchange will not recognize it. So before moving further, if you created the folder manually, delete it.
Exchange will be happy to create the folder for us automatically. All we need is to logon to the mailbox using OWA. This creates the folder, but spam will not be deposited there until Junk Email filtering is enabled. This enablement is a per mailbox setting, and can be either done manually through OWA or through scripting.
The scripting solution performs the logon and filter enablement for each mailbox. Thus it forces the folder creation and activates its functionality at one go. In this way the need to logon to OWA is eliminated altogether. Of course this is especially useful when managing multiple mailboxes.
Spam will now be deposited to the newly created folder based on the IMF configuration settings. I will skip discussing IMF. For details check
IMF SCL Configuration - getting it right.
If you are using Exchange SP2 also check the changes relevant to IMF.
Recovering a Deleted Junk Email Folder
We should now have the Junk Email folder receiving filtered spam. The experience is quite close to that provided by Outlook 2003. Nevertheless there are some important differences. Outlook 2003 is aware of this folder and handles it as a system folder. On the other hand, earlier Outlook versions lack this awareness.
This difference can be seen by right-clicking the Junk Email folder. Outlook 2003 provides the 'Empty "Junk E-mail" Folder' functionality. This deletes the entire folder content permanently. In earlier Outlook versions you can of course get equivalent results by selecting all emails and hitting SHIFT-DELETE.
A more important difference is the fact that Outlook 2003 does not permit the deletion of the Junk Email folder. Earlier versions do not recognize this as a system folder, thus deletion is not blocked. Folder deletion introduces some pitfalls to be aware of. This is indeed one of the most common support issues in these environments.
To begin with we must consider whether the folder was deleted permanently or just moved to the Deleted Items folder. If moved to the Deleted Items, Exchange will carry on delivering spam to it. You may get the impression that filtered emails are being lost. In reality these are simply deposited to the Junk Email folder located under Deleted Items. Recovering simply involves moving back the folder.
If the folder was deleted permanently spam remains unfiltered and is deposited to the Inbox. Recovering now requires a logon to OWA. As we said before this will automatically create the folder. Enabling the functionality is not necessary in this case. Again you may also opt to run the previously mentioned script for this purpose.
References
Bringing Together the Exchange Anti-SPAM Cocktail
Enabling/Disabling the Junk Email Folder
Centralizing Junk Email Folder Administration