[LINK] BigPond goes Static

[Craig Sanders]

On Tue, Jan 20, 2004 at 03:54:53PM +1100, Ash Nallawalla wrote:
> I have located people with fixed IP addresses because their email headers
> over time are unchanged.  

that's the wrong way to think about it.

people don't have fixed IP addresses.  machines do.  people just happen to
routinely use the same machine but a) people use other machines too, and b)
other people use the same machine.  so an IP address does not and can not
uniquely identify an individual.

it's not even accurate.  there are several ways (e.g. ip masquerading or NAT,
and smtp proxies) where the IP addresses in the headers do not accurately
record the source IP address.  even some mailing lists routinely strip all
received headers before re-posting a message (a dumb practice because it makes
it impossible to locate faults, but it is quite common)

also, how do you tell the difference between a fixed IP address and a long-held
dynamic IP address?  you can't, unless you know the structure of the remote
network - which, generally, you don't unless you work there as some kind of
network engineer.


> Speaking of inheriting a banned dynamic address, here is a story to dismay
> Microsoft haters.  Last week I was unable to send email with Outlook 2003 and
> I kept getting a bounce from System Administrator (Outlook itself).  The
> error message was to the effect that 203.113.202.61 is on the dsbl.org black
> list.  

That IP address is also listed by dul.dnsbl.sorbs.net, which is not surprising
because it is a dynamically assigned netspace DSL address.

> I had just acquired that address and it took me a while to realise that
> Outlook 2003 was checking the black list and denying me from sending the
> emails. 

it's more likely that the remote site was rejecting the mail when outlook tried
to deliver it.  it is then outlook's job to bounce it back to you.

> Other web apps and protocols were working fine.

that's normal.  RBLs are just lists which some mail servers use to help decide
whether to accept an incoming message or not.

> I powered down, had breakfast and restarted to get a new IP address and all
> the pending email went out as normal.  

except to sites that use one of the dynamic-IP blacklists.

with a dynamic IP address you shouldn't be sending email directly.  you should
be relaying your mail via your ISP's mail server (or, by agreement, through
some other mail server which has a static IP - there are ways of doing that
securely without being an open relay, e.g. using SMTP AUTH or TLS
crypto-certificate based relaying, or even uucp over tcp).  

at the very least, you should understand the limitations of what you are doing
and not be surprised - or upset - when your mail gets rejected because it is
coming from a dynamic IP address....because it WILL get rejected for that
reason.  there is just too much spam and too many viruses coming direct from
dynamic IP addresses for it to make any sense to accept mail from them - in my
experience, maybe 1 in a million messages from dynamic IP addresses are
legitimate, while the number of people like you who are capable of running a
mail server on a dynamic IP is miniscule (and you CAN relay your mail through
your ISP's server).  

craig