Re: [exim] Backup-MX

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Author: Dave Evans
Date:  
To: exim-users
Subject: Re: [exim] Backup-MX
On Fri, Oct 19, 2007 at 10:49:11AM +0200, Anders Hinding wrote:
> I am having a bit of a problem with configuring exim to be a backup mx
> but with a setup that only forwards mails to a certain ip-range.
>
> What I need to do is setup a mailserver that:
>
> Accepts mails from all world
>
> Only forwards mails that are sent to a domain that is based on my
> IP-ranges
>
> Bounce all other mails.
>
> The thing is that I have no way of knowing which domains are on the
> IP-ranges.


Can I check I've understood correctly please? :

If the "MX" record for the domain gives a hostname which resolves to an IP
address in a specific range, then accept that recipient (then presumably
you'll use a "dnslookup" router to send it on its way). Otherwise, reject the
recipient?

Is that correct? If so, what about the case where there are multiple MXs? Or
where one or more of the named MXs resolves to multiple IP addresses? It
sounds like it could be all to easy to end up configuring exim to be too
"open" (relaying mail which is not yours).

And I have to say I'm rather curious about the fact that you have no way of
knowing the actual list of domain names. After all, that would make the
problem a whole lot easier.

--
Dave Evans
http://djce.org.uk/
http://djce.org.uk/pgpkey