[AWG] further discussions of secondlife:/// (was Re: [sldev] [VWR] summary of VWR-4021 discussion from 2008-01-08 AWGroupies meeting & general hostname issues)

[Argent Stonecutter]

On 2008-01-12, at 11:21, dirk husemann wrote:
> Argent Stonecutter wrote:
>>
>> * As an aside, while some broken SMTP implementations use A if  
>> they can't find an MX, but they are not supposed to... if there is  
>> no MX the mail is *supposed* to bounce.
> nope: RFC 2821, 3.6

Huh.

RFC974 said you should only use MX and WKS records, and that if you  
didn't have any valid RRs you should bounce the mail (with caveats  
that an "extremely persistent" host might try to connect directly).

RFC1123 said that WKS records were deprecated, and that a sending  
host MUST provide an MX record to enable reverse mail delivery.

It's useful to be able to specify that there shouldn't be any mail  
delivery for a domain name at all, that's what "no MX records" meant.

I guess they finally decided to accept the broken behavior.  
Wonderful. At least they make it an error to use the A if there are  
any MX records present, so it's not completely broken. It's not that  
"MX is given precedence", it's that the A is a fallback if the MX is  
not present.

So you'd make a request for TXT or A, and if there is a TXT you  
should not use the A record even if the information in the TXT record  
doesn't work.