Re: [exim] dnslookup + local_domains

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Author: Mike Brudenell
Date:  
To: Exim Users
Subject: Re: [exim] dnslookup + local_domains
Hi, Bambero -

At the moment your "dnslookup" router is doing this:

1. Look up the MX record for the domain of the recipient's address.
2. From the result discard the 0.0.0.0 IP address along with any in the
127.0.0.8/8 netblock.
3. Use the "remote_smtp" transport to transmit the message to one of the
remaining IP addresses (failing between them as necessary) prioritised by
MX value.

You're seeing the error because the router is written to treat your own "
mydomain.pl" domain in the same way. So it looks up its MX record, removed
any ignored IP addresses, and ends up with a prioritised list of IP
addresses that your MX record points to.

But that list has the highest priority (lowest numbered/"use this server as
first choice") IP address identifying the machine your Exim is currently
running on!

Exim spots this and sees no point in transmitting messages to your domain
back into itself, so logs the warning.

*What to approach this…*

Remember that you can have multiple routers, with different pre-conditions
to select whether the router is chosen to handle the message or not.

For example I have two routers in my Exim configuration where the first
uses pre-conditions to identify a domain I need to deliver to using routing
information in a text file (rather than looking up MX records) and then
uses the "manualroute" driver to do this, with a second router that uses
the "dnslookup" driver to handle mail to any other domain.

You need to decide what criteria you need to decide whether a destination
server is local or remote then, I'd suggest, write two routers: one to
handle deliveries to local domains and the other to remote ones.

If you're choosing between:

- transmitting over SMTP to a remote domain's server, or
- writing the message into a mailbox on your own machine for a local user

then you likely want the routers in that order. You'll find a good example
in the standard Exim configuration file that first handles SMTP deliveries
to elsewhere, before eventually realising that anything left is to a
mailbox stored on the current server's disks and writing/delivering the
message there.

However if you're choosing between:

- transmitting over SMTP to machine's you own/are located on your own
site ("local"), and
- transmitting over SMTP to any other machine in the world

then you probably want this order instead: it's easiest to have the first
router identify "my local SMTP servers", then if that declines to handle
the delivery the second router does a normal SMTP connection to the other
site's server.

It's difficult to help as you've not explained what it is you're actually
trying to achieve, but instead have asked "how do I do X?"

Cheers,
Mike B-)

On 25 May 2016 at 22:21, Bambero <bambero@???> wrote:

> Hi,
>
> I need the following functionality of dnslookup router:
>
> 1. First always check for MX
> 2. If remote, deliver to remote server
> 3. If MX is local check in local_domains - deliver localy
> 4. Otherwise return error
>
> This order is necesairy on shared hosting where, users can add any domains.
>
> Is it possible with Exim?
>
> When I'm trying this configuration (with local_domains disabled)
>
> dnslookup:
> driver = dnslookup
> transport = remote_smtp
> ignore_target_hosts = 0.0.0.0 : 127.0.0.0/8
> no_more
>
> I got an error:
>
> May 25 22:20:58 zeus exim[22707]: 2016-05-25 22:20:58 1b5fIY-0006Uq-5b
> lowest numbered MX record points to local host: mydomain.pl
> May 25 22:20:58 zeus exim[22707]: 2016-05-25 22:20:58 1b5fIY-0006Uq-5b ==
> test@??? R=dnslookup defer (-1): lowest numbered MX record points
> to local host
> May 25 22:20:58 zeus exim[22707]: 2016-05-25 22:20:58 1b5fIY-0006Uq-5b
> Frozen
>
> Regards,
> Bambero
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