It’s pretty fair to say that admin.com is probably one of the most abused domains in the world.
I take my hat off to them in their attempt to combat spam.
They tool the simple eloquent solution of setting their MX record to localhost.
This dear reader is pure genius.
It is genius because it means that any DNS-aware mail server carrying mail for admin.com will burn up on repeated local delivery attempts my this MX record to localhost forcing the mail server into attempting delivery to itself.
The added bonus of this method is that mail never hits admin.com’s servers thus ensuring that their servers do not serve a dross of spam.
While it is obvious that this method does not allow delivery of mail if you actually want to receive mail, it is only suitable in this uncommon situation, and hmm, maybe some other situations.
It may possibly be a suitable remedy to eliciting noticeable decommissioning of domains such that the receiving SMTP servers catch no load and the sending SMTP servers get to see all the errors.
This may also be a useful spoofing technique for DNS views within your control if you want to suppress mail to certain domains within a subscribed client-base.
Or maybe suppressing mail from a machine which it is not possible to disable applications from mailing out.
A quick ‘hack’ to test this on any given machine is to alias the given domain to localhost in the /etc/hosts or c:\windows\system32\drivers\etc\hosts file in order to elicit the same outcome.
Caution is recommended – don’t lock-out access to key hosts like yourself or the device’s default router by aliasing critical network nodes. Your mileage may vary – don’t alias the name in which your machine has (if known to the device) for which you are using to administer the given device.