FAQ / Server Products

I am getting large numbers of delivery failures (or Non Delivery Reports) to addresses that don't exist on my server. Why am I getting these, has my network or mailserver been hijacked and how do I stop them?
Often spammers will pick a random domain/address to send spam from. Sometimes these addresses will be addresses at your domain and hence you will get any non delivery reports sent by the remote servers back to your server. There is nothing you can do to stop anyone spoofing an email from an address at your domain, an unfortunate limitation of SMTP.

However there are a couple of things you can do to help prevent this and also to stop the flood of non delivery reports to users that do not exist.

To help pervent spammers spoofing email from your domain, set up an spf record as described here:


This allows remote servers to check that email from your domain is actually originating from one of your specified servers.

To prevent Non Delivery Reports being accepted for users that do not exist you need to import a list of users, or setup a list of Users in the Hexamail Users section. ENSURE you have listed all users and aliases! Then go to
Hexamail/SMTP Server/Recipients
and check the box to "Restrict email to valid users, groups ..."

You will then only accept email to your actual users, and their alias.

If you still get lots of Non Delivery Reports to invalid recipients you can trap the NDRs by setting up a subject match in the SPAM Blocker, then once trapped right click them in the quarantine and choose "Block Recipient". This will add all the spoofed recipient addresses to the blocked recipient list, and your server will no longer accept email to those specific addresses.

There are also the following guides: