unwise filtering policy from cox.net

Barry Shein bzs at world.std.com
Wed Nov 21 22:03:04 UTC 2007

You're missing the point.

   xx at example.com

is going to go to whatever MX example.com returns.

Sean's point was that you can't cause, e.g., eg at example.com alone to
go to a server other than the same set of servers listed for
AnythingElse at example.com.

If that (eg at example.com) overloads those servers, even if they're
valiantly trying to pass the connection off to another machine, then
you have to use some other method like eg at special.example.com or
eg at other-domain.com and hope the clients will somehow use that tho for
BIGCOMPANY there's a tendency to just bang in abuse at BIGCOMPANY.COM.

It can be a problem in joe jobs, as one e.g.

If you think I'm wrong (or Sean's wrong) even for a milisecond then
trust me, this is going right over your head. Think again or email me
privately and I'll try to be more clear.

P.S. It's an interesting thought. The only approach to a solution I
could imagine is that the whole address would have to be passed in the
MX query.

On November 21, 2007 at 21:06 paul at clubi.ie (Paul Jakma) wrote:
 > >
 > > An unfortunate limitation of the SMTP protocol is it initially only
 > > looks at the right-hand side of an address when connecting to a
 > > server to send e-mail, and not the left-hand side.
 > > full) or the normal server administrators may make changes which 
 > > affects all addresses passing through that server (i.e. block by IP 
 > > address).
 > I guess you're saying there's something architectural in email that 
 > makes it impossible/difficult (limitation) to apply different policy 
 > to the LHS.
 > That's not correct though. The receiving MTA is quite free to apply 
 > differing policies to different LHSes. And at least one MTA allows 
 > you special-case measures applied to tables of addresses, such as 
 > whether DNSbl lookups should be applied.
 > SMTP is distributed, so you do of course have to take care to keep 
 > distributed policy consistent. But, again, that has nowt to do with 
 > LHS/RHS of email addresses.
 > regards,
 > -- 
 > Paul Jakma	paul at clubi.ie	paul at jakma.org	Key ID: 64A2FF6A
 > Fortune:
 > A plumber is needed, the network drain is clogged

        -Barry Shein

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