I administer a Windows Server 2003 with Exchange 2003 as well as GFI installed. I am watching the GFI dashboard and every third email is spam. Not only that it goes to a non existent address then the [email protected] sends out an NDR to the sender.

Should I be worried about this? I know it is directory harvesting but we have directory harvesting turned on in GFI and I do see it is working but obviously doesn't work for emails that don't exist. My issue is I would turn off NDR but then people who legitimately mistype and email address to our domain will never know their email did not get to the recipient.

What do others do to combat spam?

Is 3 times the amount of spam to ham normal?

We filter out 90% of the spam but some does get into the users inbox.

Thanks for the suggestions and advice!