Re: Email validator and mx records for subdomains

On Mar 5, 2007, at 6:37 PM, Jacob Smullyan wrote:

> On 3/5/07, Ian Bicking <[email protected]> wrote:
>> Jacob Smullyan wrote:
>>> Today someone tried to submit a form on one of the websites I
>>> maintain, entering an email address of the form
>>> "soandso-gifGjc5/[email protected]".  The Email validator, set to check mx,
>>> rejected this because forums.nyu.edu doesn't have an MX record.
>>> However, nyu.edu does and the mail would in fact be delivered.
>>>
>>> I'm not quite sure of what validation behavior would be most correct
>>> and/or useful.  Would it be better if the validator first tried
>>> d0.d1...dn.edu, then d1...dn.edu, then finally dn.edu for mx  
>>> records?
>>

The MTA is going to look up the MX records the walk the list from  
lowest to highest priority.
If no MX record is found, you look for an A record and if that exists  
try to deliver the email.
The MTA on the other side has the rules to convert spam-oupH28X6K0VWk0Htik3J/[email protected]  
to spam-B7e/[email protected]
and will reply with the corrected name in the RCPT TO.

You don't walk the domain list.


>> MTAs will start looking up higher-level DNS when there's nothing  
>> lower
>> down?  That seems pretty weird.  Is it actually that it's only  
>> looking
>> up MX, when it should look up MX and then a normal domain?  I  
>> think the
>> behavior is usually to fall back on the normal DNS when there's  
>> not MX
>> record.
>
> You must be right.
>

>> Oddly, I can't figure out what the simple way to lookup a DNS  
>> record in
>> pyDNS is.
>
> Just use DnsRequest, I think:
>
>   DNS.ParseResolvConf()
>   a=[x['data'] for x in DNS.Base.DnsRequest(domain).req().answers if
> x['typename']=='A']
>
> or something similar.
>
>
>
>
> -- 
> Jacob Smullyan
> office: 212/669-3230
> mobile: 917/576-5274
>
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