Re: [exim] Relaying and DNS lookups

>    I've been bitten by this a number of times and wondered if anyone had
>    a) done the same, and b) come up with a solution....
>    In the configuration file of our outbound mail gateway I have a host
>    list relay_hosts of all hosts allowed to relay mail. In the  ACL for
>    acl_smtp_rcpt I have the following:
>      accept  hosts = +relay_hosts
>    #
>    # If we've got this far it means the source and recipient are outside
>    our control
>    # and thus someone is trying to use us as a relay.
>    #
>      deny    message = relay not permitted
>    This is all fine and dandy until the entry for one of the hosts in
>    relay_hosts is deleted from DNS.  As Exim works its way through the
>    list to verify if a sending host is allowed to relay mail, it hits the
>    entry for the now defunct host, tries a forward DNS lookup to get an
>    IP address to compare with that of the sending host and, because the
>    lookup fails, immediately considers the sending host to not be in the
>    list thus causing delivery to fail with the "relay not permitted"
>    message.  Unfortunately, any attempt to relay mail by a host in the
>    list after the defunct host also results in a "relay not permitted"
>    rejection.
>    I'm trying to determine if it's possible to have Exim parse the entire
>    list, only rejecting if the sending IP address didn't match any of
>    those returned by looking up each host, or at the very least flag up
>    some sort of warning that the host list contains addresses that can't
>    be resolved.
>    Thoughts?
> -- 
> Paul Walsh 

> Head of Unix/Linux Systems Services,
> Corporate ICT,
> Birmingham City University,
> City North Campus, Perry Barr,
> BIRMINGHAM B42 2SU, UK 
> Tel:    +44 (0)121 331 5708
> Fax:    +44 (0)121 356 2875
> Mobile: +44 (0)7974 150 421
> -- 
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