Re: Minor isn't. It's a pardigm change

SM wrote:
> Without the implicit MX for AAAA RRs
>
> example.com.  IN MX 10 smtp.example.com.
>
> smtp.example.com.  IN A 2001:DB8::1
> a.example.com.     IN A 2001:DB8::2
>
> example.com.       IN A 2001:DB8::1
> example.net.       IN A 2001:DB8::1
>
> user.example.org.          IN A 2001:DB8::21
> toaster.example.org.       IN A 2001:DB8::22
>
> In this example, if the sending domain is toaster.example.com, we 
> would accept the mail for example.com as it fits our RFC 821 model.  
> Without the implicit MX, we would need
> toaster.example.org.       IN MX 10  toaster.example.org.
>
> for the message to be accepted.  There are valid reasons for 
> toaster.example.com to be able to send mail to a.example.com and for 
> toaster.example.org (running a SMTP service this time) to be able to 
> accept mail and DSNs without having to resort to a MX RR.  From an 
> operational point of view, let's assume that this is a short term fix 
> and we don't have the access to do a DNS change.
Excuse me for being thick, but I don't really see the problem here...

Either:
- toaster.example.org is going to send a message with the return-path of 
something(_at_)toaster(_dot_)example(_dot_)org, in which case I'd EXPECT 
toaster.example.org to have an SMTP server running on it, hence an MX 
record would not be a bad thing, or
- toaster.example.org is going to send a message with a null return 
path, in which case what does it matter..
Personally, I can see a strong point for requiring MX records for any 
domain which can receive mail as it removes a big ambiguity. Anyone who 
doesn't set one up will soon notice that things aren't working and will 
fix it. If a mail administrator is on 'talking terms' with the DNS 
administrator enough to have an AAAA record assigned to them, surely 
they're on talking terms enough to have an MX record set up as well, 
especially since the DNS administrator should know enough to know that 
one is expected.
Maybe some people would automatically set up an MX record for every AAAA 
record, to get the equivalent behaviour as for IPv4, and there's nothing 
wrong with that if they want to waste resources, but I'd expect most to 
be more sensible and just set them up as necessary.
A possible alternative could be to change the retry requirements for 
domains which don't have an MX record, so you do a '3 day' retry for 
domains with MX records, but a shorter retry for domains with only AAAA 
records - this would avoid the big problem of people sending mail to 
domains which are never going to accept mail, and thus the massive 
resource wastage due to all the failed retries which are doomed to 
failure. The bad side of this is that the 99% of people who don't read 
the standards will think things are working OK without the AAAA domain 
when they're only partially working - hence I'd think the mandatory MX 
record would be a better idea.