Suppose a spammer registers a domain spammers-r.us, adds these DNS records:
spammers-r.us MX 10 mail.spammers-r.us mail.spammers-r.us A 127.0.0.1
This is exactly what I have already seen at least once with a mainsleaze spammer. I can't find my notes, so I cannot confirm this, but I do remember that it caused my MTA issues (basically mailbombed itself trying to bounce a message).
It would be wise to try and program with this evil behavior in mind...
John
