[Mimedefang] Am I overlooking something in my filter_relay method

Jan-Pieter Cornet johnpc at xs4all.nl
Sun Jul 16 06:37:09 EDT 2006


On Sun, Jul 16, 2006 at 11:02:06AM +0200, ML Listuser wrote:
> So I created a filter_relay which, on a connect-request, tries to establish a
> telnet/smtp connection with the calling host and if it does _not_ succeed, 
> rejects the connection with '554 <my mx> ESMTP not accepting messages'.

You wouldn't be able to receive mail from us: xs4all.nl (and all
customers and customer domains). Several other largish ISPs might
have the same problem.

Our outgoing smtp server is actually a loadbalancer, spreading
the connections over several client machines. The client machines
cannot receive incoming SMTP connections, since they are for outgoing
SMTP only.

This setup is not unusual, separating outgoing and incoming SMTP
servers; And often the outgoing SMTP servers will not allow incoming
connections.

John Rudd's suggestion might make more sense, blocking on dynamic-
looking hostnames. However that isn't ideal either, because it will
block wellbehaved SOHO mailservers on DSL lines from really crappy
providers (without properly functioning outgoing mailservers,
and without a possibility to change the reverse DNS name).

-- 
Jan-Pieter Cornet <johnpc at xs4all.nl>
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