Le 16/07/2016 à 11:11, Lefteris Tsintjelis a écrit :
> On 16/07/2016 11:35, Jim Reid wrote:
>> That wouldn’t have worked anyway.
>>
>> Assuming a reverse lookup of an IP address returns a name -- a big if
>> -- there’s no guarantee that name has any relation to whatever domain
>> name is in the MAIL FROM.
>>
>> For instance, lots of organisations outsource their email to
>> specialised hosting/service providers. A MAIL FROM might well say
>> example.com while the reverse lookup returns some name in
>> $emailprovider.com for a server that’s delivering email sent by
>> bazillions of customers.
>
> No guarantees of course but the majority of valid MX servers return a
> name.
>
> It would have worked for smaller orgs where they usually have one MX
> server and a relativly simple mail and domain setup. Besides, this would
> have been a white listing only method so no harm done other than the
> additional DNS lookups but I guess it is not postscreen's job for this.
>
MX are for *incoming* messages. No garantee at all that outgoing servers
are the same. For big companies, it is quite standard to use different
servers for incoming and outgoing messages.
