On 7/17/11 10:22 PM, Always Learning wrote:
>
>> Multiple interfaces, multiple IP addresses. Sendmail isn't going to track which
>> interface it is sending on and adjust its greeting.
>
> Sendmail ? Golly some of us have advanced to more advance systems like
> Exim ;-)
Does it vary it's HELO per interface? How is it aware of upstream NATs?
> When I complained to Cable& Wireless who operate mail sending from all
> the UK police forces, they adopted a seemingly unique solution by having
> the identical host name mapped to their different IP addresses. That
> solution solved it for me.
I'm somewhat shocked that they made such a change when there is no standard that
requires it.
> It is not inbound (to them) that interests me but outbound. Every IP
> address can have a host name, so in theory there is no reason for the
> use of fake (non-existent or wrong) host names when sending emails.
IP addresses do not correspond to hosts. They correspond to interfaces. There
is not a 1 to 1 correspondence between hosts and IPs.
> When a computer application is configured to send emails, part of the
> configuration process permits a host name to be chosen. In theory there
> seems no sensible reason for a fake host name to be used and that must,
> I would have thought, apply to multi-homed, clustered, load-balancers
> etc. There is absolutely nothing to stop several IP addresses having the
> identical host name.
If you like to waste IP addresses, you could add some just to give them names
that would keep you happy.
>> Just because it doesn't match the IP doesn't make it fake.
>
> There are three reasons why a host name may not match the IP address it
> is operating on.
>
> (1) there is no A record so that host name does not exist;
>
> (2) there is no reverse name for the IP address;
There isn't much correspondence between 1 and 2 either. The host name, the
forward DNS entry and reverse DNS entry are all very different things, generally
managed by different sets of people, even in cases where there is a one to one
correspondence, which there often isn't.
> (3) the host name belongs to a different IP address;
Or many of them.
> Bogus host names are simply a symptom of a disorganised and neglected
> mail sending (and perhaps also receiving) system where no one takes any
> pride in doing an important job responsibly.
Or people following what the standard says and expecting others to do the same.
--
Les Mikesell
lesmikesell at gmail.com