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

2008-03-31 02:57:24

SM wrote:
Without the implicit MX for AAAA RRs  IN MX 10  IN A 2001:DB8::1     IN A 2001:DB8::2       IN A 2001:DB8::1       IN A 2001:DB8::1          IN A 2001:DB8::21       IN A 2001:DB8::22

In this example, if the sending domain is, we would accept the mail for as it fits our RFC 821 model. Without the implicit MX, we would need       IN MX 10

for the message to be accepted. There are valid reasons for to be able to send mail to and for (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...

- is going to send a message with the return-path of something(_at_)toaster(_dot_)example(_dot_)org, in which case I'd EXPECT to have an SMTP server running on it, hence an MX record would not be a bad thing, or - 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.