[Mimedefang] Revisit: Filtering on HELO

Philip Prindeville philipp_subx at redfish-solutions.com
Sat Mar 24 01:20:36 EDT 2007

Les Mikesell wrote:
> Many hosts are multi-homed and thus have more than one address.  I don't 
> think mailers are required to match the HELO to the interface that 
> happens to be used for the connection.  Also in the NAT case it may or 
> may not be possible for anyone to know the address that will be seen on 
> the other side.

That doesn't matter a whit.

Under the Posix (sockets) interface, you create a socket(),
initiate the connect() to the remote host, then you can do
a getsockaddr() to get the *local* address that the socket
was bound to when the outgoing interface was selected
during the connect.

Which is who you announce yourself to be.

(In fact, it might even have been a host-requirements
bullet that required that multi-homed hosts know which
interface--and address--they were speak via.)

Remember: the original requirement of the HELO command
was to avoid mail loops by helping a host identify when it's
looped back on itself.

That logic would fall on its face if the host didn't identify
what interface of itself it was using when it sent the


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