Re: Mx lookup

-------- Original Message  --------
Subject: Re: Mx lookup
From: Mark Blackman <mark <at> exonetric.com>
To: Charles Marcus <CMarcus <at> Media-Brokers.com>
Date: Wednesday, May 14, 2008 9:41:51 AM
>
> On 14 May 2008, at 15:34, Charles Marcus wrote:
>
>>>> Just log into your OpenDNS account and disable 'Typo Corrections' and
>>>> you're good to go...
>>
>>> Thanks, I certainly didn't realize that option existed, but
>>> how does that deal with malicious conflicting IP entries?
>>>
>>> i.e.
>>> user A declares they do queries from IP A and turn off typo correction
>>> user B declares they do queries from IP A *as well* and turn *on* typo
>>> correction.
>>
>> ? What do users have to do with it? This is on a server. If you have
>> your mail server DNS pointed at OpenDNS, it simply uses OpenDNS. You
>> need to have an account with them (free), which is associated with your
>> IP address(es) in the 'Networks' section.
>
> I don't think it's uncommon to have a postfix system sitting behind
> a NAT IP address with a public IP address shared by web clients
> in the same office. First person to sign up with that *shared* public IP
> address controls the settings as far as I can tell and that might not be
> the system administrator.
>
> - Mark
>
>
Perhaps someone should contact OpenDNS, as mx lookups may not be 
suitable for "typo correction". The reasons being that 1) it breaks 
software that rely on nxdomain responses (specifically common in MTAs); 
2) even if an email made it to the intended destination server, that 
server would likely reject the message because the domain or mailbox 
doesn't exist (because of the typo).

e.g. I email user5 <at> gmaill.com -
Oh no, gmaill.com doesn't exist, but typo correction saves the day and 
figures out you meant to send to user5 <at> gmail.com
Your server sends to gmail, but oh wait! gmail.com's mail servers don't 
accept email for gmaill.com, your message is rejected.

This detection could have happened earlier and the message never left 
the sender's client... I don't see any win for using typo correction on 
MX records... AGain, perhaps a registered user of OpenDNS could let them 
know about this issue.

-Blake