On 29 Mar 2008, John Levine wrote:
to non-mail domains is significant. I have at least one host name
that was never a mail domain, but since it used to appear in usenet
headers it gets over 30,000 spams a day, every day.
I'm not convinced you've identifed causality ... only correlation. I
suspect that many spam sources routinely 'scan' for open port 25s and
send mail .. if a connection is accepted, they assume they have a mail
server. If they want a dns name for the email, they do a rdns lookup.
Nothing about the assumed fallback to A or AAAA will effect that form of
address lookup. Don't listen on port 25 if you don't want the mail. For
your web mail, make the right headers so that a reply will work. Or
arrange to have the mail depart from a valid mail server. If the recipient
of your of your emails replies back, and they get a rejected message, in
15 minutes or 5 days, either way it won't be something they will know what
to do with if they didn't know in the first place to not send to that
address. Better to improve the basic design than to expect in 10 years
when there are no IPV4 systems left that they will finally get near time
notifications of a delivery failure. Or perhaps define a new ICMP message
which some new revision of the mail protocol will define means to
immediately return the email.
It is true that most hosts don't run mail servers ... but the corollary is
that the host names will be used in published email addresses so it may
not matter all that much than random typos result in a missfire to an A
record or AAAA record defined host.
On a side note ... there is a lot of tooth knashing re. slow adoption of
IPV6 ... simple fact is that EACH procedural incompatibility introduces a
small issue in the minds of folks who have to manage the conversions and
roll out. Will slow down adoption because of perceived increased support
Of course, it could end up like NAT ... ignored for purity reasons by
the IETF, but used in practice... one more way the IETF margninalizes
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