We're using Exchange 2010. We have a user who is receiving thousands of NDR messages from our Exchange server as a result of a spammer using his address to spam a ton of Yahoo and Hotmail addresses.
I've tried disabling NDR messages under Remote Domains, I've enabled RecipientValidation, no dice. How can I prevent Exchange from generating these emails?
You can't, because it isn't Exchange generating them.
The remote server is generating the messages and then sending them to your server. Your server has to accept them - attempting to block/reject them will simply cause your server to be blacklisted.
Configure SPF and DMARC records - that should help to some degree. However as you are receiving the NDRs, the real problem is the remote servers are not setup correctly to filter invalid recipients (which is probably what most of the NDRs are). Therefore they are probably not using SPF records either.
You may have to simply weather the storm - it does stop eventually.
Recipient validation wouldn't help because the recipient is valid.
Setup a transport rule to drop the message without notification when the recipient matches
[email protected]and subject or body containsblah blah blah.I don't have 2010 in my environment any longer so I can't give explicit instructions on how to do this. Hopefully that starts you in the right direction.
You might not want to keep this in place forever.