On Sun, 13 Aug 2000, Chris Holt wrote:
> On 12-Aug-00, Fred Wright wrote:
>
> >> I think I pointed this out before, but my ISP does not own the POP that
> >> is here. The DNS lookups work but the DNS servers that are returned do
> >> not belong to Earthlink. Everything works when I leave DNS on automatic,
> >> with the exception of sending mail. The SMTP server checks somehow, and
> >> does not consider me to be "dialed up" to earthlink, much as if I tried
> >> to use it from the LAN at work. I have seen several other services that
> >> use the same POP as earthlink, and they all prefix the logon somehow.
> >> For example, my earthlink logon is "ELN/digitalq". Now I'm assuming here
> >> that if the machine that is used there can tell I belong to earthlink,
> >> then it could somehow be told to spit back DNS servers that are owned by
> >> earthlink, but I don't know.
> >>
> >> Should I complain? I am, after all paying them for the service.
> >>
> >> I think that if they change the DNS IPs, it would be pretty obvious
> >> though.
> >> So I just call them up and find out the new ones, right?
> >
> > It's not necessarily true that you need DNS servers associated with your
> > ISP. What you want is reliable servers "close" to your POP that give the
> > correct answers. Whether they should belong to your ISP or the party
> > that's supplying the POP depends on the architecture.
>
> I see.
>
> > The SMTP server itself is completely unaware of your DNS settings, but I
> > can think of a few ways the DNS choice might come into play:
> >
> > 1) You're using a fully qualified domain name for the SMTP server, but
> > the different DNS servers are returning different IP addresses for it,
> > and hence you're actually using different servers. IP<->hostname mappings
> > aren't *supposed* to vary with the server, but various misconfigurations
> > are possible.
>
> The SMTP server is found, that is not the problem. The server returns
> "relaying denied" if I have anything other that the supplied DNS servers
> in my database. Including the ones that get "looked up" at logon.
Well, *an* SMTP server is found. The question is whether it's the *same*
SMTP server in both cases.
> > 2) You're not using an FQDN, and the server name is being looked up in
> > different domains as a function of the DNS server chosen (perhaps due to
> > the "auto-add domain" feature), thus again yielding different IPs.
>
> Same as #1, I think. Attempts to logon to the SMTP server are greeted with
> "relaying denied"
Yes, same as #1, and same question.
> > 3) You're getting the same server each way, but your hostname is being
> > set up differently as a function of the DNS server, and the SMTP server
> > is being fussy about this.
>
> Aha, this sounds like what they must be using to deny access from outside
> the domain.
>
> Yep! Just checked. Turned "Get DNS" back on, connected and put the
> numeric IP of the SMTP server in YAM and the domain set to
> "earthlink.net". Mail was sent without incident.
That doesn't prove it's #3. In fact, it makes it *more* likely that it's
#1 or #2, and you're getting a different IP for the SMTP server depending
on ahich DNS server you use. Again, check with MiamiResolve or perhaps
use MiamiNetStat -n shortly after sending a message.
What you changed in YAM was the address of the *server*, but the hostname
issue concerms the name of the *client*.
> So this tells me that thier reason given for this behaviour (eliminating
> the relay of mail through thier servers for bulk mail purposes) may be a
> noble cause, but it is all to easily circumvented. It would only seem to
> cause grief for thier customers, and neophyte spammers. :P
Indeed, but I don't think this is what's happening, as noted above.
Fred Wright
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