Re: [Exim] 550 DNS FAILURE with aol

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Author: Greg Ward
Date:  
To: exim-users
Subject: Re: [Exim] 550 DNS FAILURE with aol
On 11 August 2001, Scott said:
>
> I get this error when sending to anyone at aol. This is the only smtp I
> have problems with. Im on a DSL line (reverse comes back to swbell)
>
> This message was created automatically by mail delivery software.
>
> A message that you sent could not be delivered to one or more of its
> recipients. The following address(es) failed:
>
>   validusername@???:
>     SMTP error from remote mailer after MAIL FROM:<dontspam@???>:
>     host mailin-04.mx.aol.com [152.163.224.122]:
>     550 REQUESTED ACTION NOT TAKEN:
>     DNS FAILURE


My guess is that AOL doesn't like the fact that your IP address doesn't
reverse-resolve to your claimed hostname. Anyone using a dialup, DSL,
or cable-modem connection has the same problem. (AFAIK ISPs haven't yet
clued in and started offering dynamic DNS service, with reverse
resolution, to their customers...)

The usual solution is to use your ISPs SMTP server as a smarthost. The
cool thing about Exim (OK, one of many cool things about Exim) is that
you can choose to connect directly to certain domains -- circumventing
your ISP -- and to go through your ISP to others. This is done with a
domainlist router; here's mine:

smarthost:
  driver = domainlist
  transport = remote_smtp
  route_list = "mems-exchange.org mems-exchange.org bydns ;\
        bic.mni.mcgill.ca bic.mni.mcgill.ca bydns ;\
        * relais.videotron.ca byname"


end

Mail to *@mems-exchange.org or *@bic.mni.mcgill.ca (my current and
former workplaces, so I tend to send a lot of mail to both domains) goes
straight from my PC (cable-modem connection, dynamic IP address,
meaningless reverse DNS) to whatever MX Exim finds for those domains.
Mail to anyone else in the universe ("*") goes through my ISP's SMTP
server (no DNS lookups and no MX records because I said "byname").

This works great for me...

        Greg
-- 
Greg Ward - software developer                gward@???
MEMS Exchange                            http://www.mems-exchange.org