Exchange 2010 SCL Filtering with Internal SMTP Smart Host

Posted on 2014-09-09
Last Modified: 2014-09-12
I have an SBS 2011 server running Exchange 2010 that utilizes an SMTP smart host that receives all inbound email which then forwards to the Exchange server.  What I have noticed is that none of the content filtering I have enabled on the Exchange server is working and applying SCL ratings because the smart host is internal and on the same domain.  After researching this scenario it seems that Exchange by default will not filter any internal email.  I would like to change this and allow Exchange to apply an SCL rating on inbound mail that it receives from the smart host.  What would be the proper configuration to achieve this and force Exchange to apply the SCL content filtering?  

Any information is appreciated.  

Thank you
Question by:ColumbiaMarketing
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LVL 63

Accepted Solution

Simon Butler (Sembee) earned 500 total points
ID: 40313368
If you have a smart host accepting email from the internet, that is really where the spam filtering should be taking place. Trying to do it at Exchange is much too late.

To answer your specific question, you cannot change the behaviour of Exchange. Exchange is expecting to either be the primary receiver of the email, or a host to be in a DMZ, so a separate IP address range.


Author Comment

ID: 40314909
Thank you for the information.  I should clarify my goal with this.  There is a small amount of spam that will make it through the smart host and since Exchange is not rating any emails from it the spam will be put directly into the Inbox folder.  Ideally, if Exchange could tag messages from the smart host with an SCL rating I could then mitigate this by filtering potential spam into the Junk E-Mail folder rather than the Inbox within Outlook.  Or is this method not the best practice?  I would like to handle this from the Exchange server itself rather than configuring Outlook's own spam filtering on a per user basis to filter potential spam to the Junk E-mail folder.  

Maybe configuring a GPO for Outlook spam filtering to be more aggressive would be a better way to handle this from the server.
LVL 63

Expert Comment

by:Simon Butler (Sembee)
ID: 40318139
Thinking about it again  - it should be working as you have outlined, as there are loads of posts on this site about IMF catching messages from scanners etc. If you look at one of the messages, does it have any SCL value? Maybe the message that is getting through wouldn't be blocked by Exchange either.


Author Comment

ID: 40319623
Yes, by default it will tag the messages with a -1 SCL rating, which is basically the equivalent of white listing.  After checking with an engineer at Microsoft it seems that this is by-design and can not be changed for internal email.  So handling this from the server side really isn't practical in my case.  Although the option of increasing the spam threshold in Outlook would be an alternative.  

Your notion of handling all filtering at the smart host would be correct in my situation as this is the way Exchange is designed to run when utilizing a smart host on the same internal network.    

Thank you for your help.

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