Re: [Exim] Refuse connection if no MX for sending host

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Autor: Exim Users Mailing List
Data:  
A: Tony Finch
CC: rduvall, exim-users
Assumpte: Re: [Exim] Refuse connection if no MX for sending host
[ On Thursday, October 23, 2003 at 11:59:26 (+0100), Tony Finch wrote: ]
> Subject: Re: [Exim] Refuse connection if no MX for sending host
>
> So in most cases there's no direct relationship between the machine's
> hostname and relevant MXs -- this is even more evident in the Demon
> case where the customer domains are in demon.co.uk but the machine
> names are in mail.demon.net. Note also that it would be wrong to have
> an MX for plum.csi.cam.ac.uk since there are no valid email addresses
> @plum.csi.cam.ac.uk.


That's wrong. There is always at least one valid mailbox address at
every mail server that answers and speaks SMTP on port 25 (and it _must_
be valid for both the host name of the mailer as well as for a domain
expressed as a literal IP address).

There _should_ always be an MX for every domain name that is a host name
of a mailer, and the target name of the MX should be the same domain
name:

    mail.weird.com.        IN A    204.92.254.2
                IN MX    1    mail.weird.com.


Anyone too lazy or ignorant to configure the DNS for their mailers in
this way is doing a disservice to the Internet community.

That said I will note that even on my home system I don't check for an
MX for the sending client host. Checking that the helo name resolves to
the client's source address is sufficient.

--
                        Greg A. Woods


+1 416 218-0098                  VE3TCP            RoboHack <woods@???>
Planix, Inc. <woods@???>          Secrets of the Weird <woods@???>