Exchange Server 2013 introduces a change that has an adverse effect on the Outlook junk email filter feature. The end result is that messages excluded from junk email evaluation in earlier versions of Exchange Server and in Office 365 pre-upgrade environments are now evaluated and potentially moved to the Junk E-mail folder.
Outlook and Exchange use a MAPI property (PR_CONTENT_FILTER_SCL) to control the behavior of junk email features in Outlook. Specifically, Exchange can set this property to a value that tells Outlook to exclude the message from client side junk email scanning. This property is referred to commonly as the “SCL” for the message.
With Exchange Server 2013 and Office 365, Outlook does not use the SCL value from the Exchange Server.
The following results apply:
Important This does not mean that all email messages always go to the Junk E-mail folder. However, they are not automatically excluded from junk email processing. The junk email filter will still make a decision, and some email messages may appear to work fine, while others go to the Junk E-mail folder. This includes email messages sent from an external trusted domain addresses for which SCL is set to -1 by using an Exchange Transport Rule or the IPAllowList. Also affected is internal email from process servers or custom applications that use SMTP.
This issue is fixed in the Outlook 2010 hotfix package that is dated February 11, 2014. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
2863918 Description of the Outlook 2010 hotfix package (Outlook-x-none.msp): February 11, 2014
This issue is fixed in the Outlook 2013 hotfix package that is dated April 8, 2014. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
2878323 Description of the Outlook 2013 hotfix package (Outlook-x-none.msp): April 8, 2014
If you are unfamiliar with the application and management of SCL -1 as it relates to Exchange Server 2010 and later versions, please see Tom Kern’s excellent post on the Exchange Team Blog:
Accepted Domains, Safe Senders List and You
Is there any news on this issue? We are experiencing it with our Office365 Tenant. Mails with SCL -1 will be moved to Junk E-Mail-Folder sometimes.
It started for us after we came back from Christmas break. We're using Exchange 2010, but Outlook 2013.
Everyone, please note that this post has been updated to include the hotfix details for Outlook 2010.
Please note that this post has been updated to include hotfix information for Outlook 2013.
great! Glad to see this is fixed in 2010 and 2013. Will this hotfix be rolled out automatically with office updates?
Eventually, when a public update is released for Outlook 2010 or Outlook 2013, it will include this fix. Public updates automatically appear in Windows Update.
Atleast in my own Exchange 2013 environment running Outlook 2010, the only way I could get this resolved was to disable "Cached Exchange Mode." Even without the Hotfix installed, all mail is being routed normally again.