Re: Sender header?

[prj@po.cwru.edu (Paul Jarc)]

Harry Putnam <reader@newsguy.com> writes:
> prj@po.cwru.edu (Paul Jarc) writes:
>> > Currently I've told gnus to stick my IP smtp server address in
>> > Message-ID.
>> 
>> Don't do that unless you control the SMTP server, and know that it
>> won't generate Message-IDs using that same RHS.  See my other message
>> for more details.
> 
> Now I'm really confused..
> Wait... shouldn't that smtp server AlWAYS use the same rhs?

Probably.  But if you control it, you could configure it to do
otherwise.  The main principle is that two different hosts should use
two different domain-like things for their Message-IDs.  So if you're
using your SMTP server's hostname to generate Message-IDs on a
different host, then you should make sure that the SMTP server doesn't
use the same thing.  If you don't control the SMTP server, then you
can't ensure this, and so you should use something else on your other
host.

> The machine has a name like (/etc/hosts entry):
> reader.local.lan        192.168.xx.xxx   reader
> There must be several (100/1000 ?) that could possibly have that FQDN.
> How is this uniqueness obtained?

Normally - i.e., "normal" at the time Message-ID was designed - you'd
have a static FQDN on the Internet, and you'd use that.

If possible, you should set things up so that Message-IDs are
generated by hosts with static FQDNs on the Internet, and those hosts
should use (probably) their own FQDNs for the RHS.  Hosts that don't
have static FQDNs should pass along the message without a Message-ID,
and the the host that has the static FQDN generate one.  This may
require special configuration on both sides.

If you can't do that, then try to use the FQDN of a host with a static
FQDN on the Internet and which you control, so you can tweak each of
their generation algorithms, if necessary, to ensure that the two
won't ever generate the same LHS by accident.

If you can't do that, then you're stuck, and all you can do is make a
best effort.  Throw some entropy into the RHS (maybe something like
o4igh2r3.username.this-does-not-exist.your-isp.com, where the first
part is preferably different for each message), and explain to anyone
who objects that Message-ID was not designed with your situation in
mind, and this is the best you can do.

> Hard to see how either of these can be guarranteed to be unique any
> more than:
> Message-ID: <m1hey9z673.fsf@super.clever.insertion>

They can't, except that by convention, the RHS is at least based on
the FQDN of the Internet host where the Message-ID was generated.  If
you stray too far from that convention, you run the risk of choosing
the same clever insertion that someone else did.  Stay as close to it
as your situation allows - if you can use a host's FQDN, use it;
otherwise, use your organization's domain name along with something
which is unique in that context, etc.


paul