Link to home
Start Free TrialLog in
Avatar of jag b
jag b

asked on

exchange 2013 - bounce back messages not working

Hi guys,
I have exchange 2013 - infront of this i have websence hosted email security - when an external user sends an email to an incorrect user in our domain or to a random address the sender is not getting no bounce back - have checked websence and the logs show our exchange has accepted the email.  However internally the bounce backs works fine....
ASKER CERTIFIED SOLUTION
Avatar of Simon Butler (Sembee)
Simon Butler (Sembee)
Flag of United Kingdom of Great Britain and Northern Ireland image

Link to home
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
Start Free Trial
Avatar of jag b
jag b

ASKER

Hi simon,
thank you for your reply - further information as below:
On my send connector I am going through a smart host - when I change this to MX record associated then ndr's work fine.... issue with the smart host?  
Is it ok to use the MX record associated with recipient domain?
The fact that you are able to send the NDRs directly suggests that the smart host is rejecting them.
However it also means you do not have recipient filtering enabled and what you want to do is called backscatter, which will get you blacklisted.

As I wrote above, you should configure the Websense service to reject emails for non-existent senders. Not accept them and then allow Exchange to generate an NDR.

By accepting emails for any recipient and then attempting to NDR them, you are exposing your server to an NDR attack. This is where a spammer sends emails to your server to non-existent recipients on purpose, so your server bounces them to the sender. The sender is spoofed and is the actual target of the spam run. Therefore not only do you get blacklisted, but you end up with a lot of emails in your queues to bad email addresses.

Simon.