Anti-Spam gateway for Exchange 2010

How do you expect any software / device to be able to determine Invalid Recipients on an outbound email before it has actually sent the email?

Barracuda Spam & Virus Firewall

check if this works for you

http://techlib.barracuda.com/display/BSFV51/Step+1%3A+Understand+the+Concepts

@Alan.
I know there are some solutions that offers that. Spamexperts for example allows you to limit number of allowed invalid recipients. Technically speaking it can be done.
Question, assuming there aren't too much solutions that can provide this protection, how do you handle with users who mass emailing other domains assuming they pass all other spam mechanisms?

@Haresh,
Thanks, I was just finish talking with Barracuda salesman, so far it seems good.

I use Trend Micro Worry Free Business Security Advanced.

This package included antivirus and antispam client for PC's and server.

It also inscluded Hosted Mail Security (spam filtering)

and also exchange message scanner.

Works great and of course there is a web login so you can edit whitelists and unquarrantine mails as well as set up outbound security etc

http://www.trendmicro.com/us/small-business/product-security/

Not sure about the invalid recipients thing, but we use Mimecast, which is a service that sits outside our environment and filters both directions. We went to it last year after being a Postini customer for years and so far really like it.

Whatever methods SpamExperts are using to try and establish that the recipient is bad before or during sending, isn't going to be very reliable, and I would drop it from your list of requirements. There is a reason why no one else does it.

The only way they can establish that (if indeed they do it), is to attempt to see the result of sending the email to the recipient server. Any email admin who is doing their job properly is going to be using tarptting, because that is also a job that spammers want to do, as a valid email address is worth more. Tarpitting will slow down email delivery for anything from five seconds onwards, if it is even allowed to continue.

As for users mass emailing other domains, simply restrict the number of emails that can be sent by a single user. Mass emailing should either be banned completely or outsourced to a bulk email provider.

Simon.

For mass mailing it is better to use a 3rd party list server.. you provide the list of email addresses and the content and you let them send on your behalf.

Hi,

thank you for your comments.
I found out in the smtp logs that the sender did not mass emailed at once.
Instead the logs show that all those emails were send in a matter of seconds:

22:29:16 ,550 Message was not accepted -- invalid mailbox
22:29:18 ,550 Message was not accepted -- invalid mailbox
22:29:19 ,550 Message was not accepted -- invalid mailbox
22:29:21 ,550 Message was not accepted -- invalid mailbox
22:29:25 ,550 Message was not accepted -- invalid mailbox

So how can this be avoided using Spam engines?
Also, is there a way in outbound filtering to whitelist keywords in the email content?