Re: Problems with mail system? [Fwd: Returned mail: User unknown]
On Thu, Sep 07, 2000 at 06:09:31PM +1100, Craig Sanders wrote:
> nobody's telling anyone to get any particular ISP or that they have to
> pay for a premium quality service.
> it's simple - if you want a service that's worth having, you pay
> whatever it costs. if you don't want that, then pay for a cheap/crappy
> service and put up with it without whining.
> (that said, i don't believe that missing reverse DNS is a good
> reason for bouncing mail. a "450 try again later" response is more
> appropriate, to cope with temporary dns outages. bouncing mail from
> nonexistant domains, however, is a different story - it's almost
> certainly spam and there's no point in accepting a message which
> doesn't have a valid reply address so just bounce it)
Ouch. I think debian developers should have a better understanding
 A mail domain does not have to have a valid IP address.
As a default, if you use a mail domain for which there's no mail exchange,
the default is to look for a host address with that name. But that's
just the default.
 A PTR record does not have to contain *any* information whatsoever.
Imagine the mail client at 18.104.22.168 initiates an smtp session with
your system. Your mail server performs a PTR lookup and gets back
22.214.171.124.in-addr.arpa. It then performs an A lookup and finds that
126.96.36.199.in-addr.arpa has the address 188.8.131.52. What have you learned?
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