anti spam policy - hub transport server or edge transport server

i have an environment where the edge transport server is a Linux Box with Sendmail installed on it ... Currently, there is no anti spam thing on that box (as I havent read details on how to do that in Linux) ... Next, I have a hub transport server which is Exchange 2007 that delivers all teh emails to my domain's email addresses ... I dont have an anti spam configured there as well ...
I would like to general recommendations on where should anti spam policy be defined ? Edge transport server or Hub transport server ? from the concept, it makes more sense if we define it on Edge transport (i.e. the Linux one) .. But is there any downside if i dont define any anti spam policy there on Linux Box and simply define it on my Hub transport server which is Exchange 2007 ? Whats the drawback (if any) in doing so ?
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Can't help on setting up Linux as I don't use the product.
If the Linux box cannot do even recipient filtering then I would be looking to remove it, as it is not assisting any way. Have email delivered directly to the Exchange 2007 server which can do the most basic of antispam filtering in a more efficient manner.

If you don't block messages at the point of delivery you are wasting a lot of bandwidth in having messages delivered to your server that you don't want, and as I have already pointed out, if you then attempt to reject those messages you will cause back scatter and get yourself blacklisted.

While I appreciate that you want to get rid of spam in to your users inboxes, if you do not do it correctly then email that your users SEND will fail to be delivered or will be filtered as spam as well. Spam fighting is not a one way street.

If you don't have an Edge server then the antispam agents are installed by running the installantispamagents.ps1 script. You then need to configure them. It is not something that works straight away.

Anti spam should always be done at the point the email enters your network. At the very least you want to do some kind of recipient validation so that you drop email for non-existent users at the point of delivery, rather than after delivery has taken place.

If the antispam takes place later on, then the spammer has already used your bandwidth to deliver the message, and if you bounce the email you are causing back scatter.

nabeel92Author Commented:
Ok, I agree with what you're saying. That's exactly how it should be.

but  for the time being we dont have any anti spam policy defined on linux sendmail which is acting as edge transport, so can i define anti spam on my hub transport server in the meantime (which is an exchange 2007) ? Although it contradicts to what you're saying but if the priority is to rid of spam getting delivered in the inbox and priority is not following THE PERFECT DESIGN or bandwidth ? is it workable to define anti spam on hub transport role or are there any downsides to it still ? Your recommendations ?

Secondly, correct me if am wrong but I think how we define anti spam on Exchange 2k7 is to run antispanagents.ps1 from power shell and restart Microsoft transport service ? am a new comer to Microsoft.

Any link for configuring anti spam policy on Linux Sendmail would be even greatly appreciated !

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