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.