[CentOS] SPAM on the List

Les Mikesell lesmikesell at gmail.com
Mon Jul 18 02:57:11 UTC 2011

On 7/17/11 9:18 PM, Always Learning wrote:
>>> Legitimate senders should not use fake, false, misleading credentials.
>> There is no requirement for the greeting name to match any IP, and isn't likely
>> to work for multi-homed and/or clustered machines.
> Which type of 'multi-homing' were you thinking about ?
> http://en.wikipedia.org/wiki/Multihoming
> * Single Link, Multiple IP address (Spaces)
> * Multiple Interfaces, Single IP address per interface
> * Multiple Links, Single IP address (Space)
> * Multiple Links, Multiple IP address (Spaces)

Multiple interfaces, multiple IP addresses.  Sendmail isn't going to track which 
interface it is sending on and adjust its greeting.

> Which type of 'cluster' were you thinking about ?
> http://en.wikipedia.org/wiki/Computer_cluster
> * High-availability (HA) clusters
> * Load-balancing clusters
> * Compute clusters
> If any of these share the same IP address, they can share the same host
> name.

There are any number of topologies that use multiple IP addresses for what 
appears to be one name.  A load balancer might be involved, they may or may not 
accept on the same IP's as they use for outbound connections, they may or may 
not know the outbound ip.

> I am not well acquainted with either of the above two methods,
> multi-homed and clusters, but I can not understand why any of them
> should resort to using fake identities when sending-out emails.

Just because it doesn't match the IP doesn't make it fake.

> Can you help me understand why bogus identities are necessary in these
> circumstances ?

You are the one defining it as bogus.  Consider a system where one or more of 
it's routes to the internet go through nat routers or the nat functionality of a 
load balancer.  The program sending the mail won't even know the IP you see.

   Les Mikesell
    lesmikesell at gmail.com

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