> Many mail servers are lenient when it comes to this misconfiguration and will deliver mails nevertheless, so this may stay undetected. I happen to use a mail server that is less forgiving (Courier), and every now and then I cannot send a mail due to this.
Sorry man but this sounds like a "you" problem. You probably need to fix your mail server or get a new one.
1. Accept that the new standard is that ip addresses should be supported, and write a new rfc document with that change.
2. Encourage people to not support this.
Simply asking all mailservers to support this non-standard feature (or de facto standard) is arguable the worst outcome, because now every mail server implementer is expected to implement the standard + a bunch of institutional knowledge.
Luckily with mail there's a lot of incentive to set things up correctly, because getting parts of it wrong likely results in a higher number of emails going to spam.
And here we see someone exemplifying why Gresham's Law trumps Postel's Principle. Bad protocol implementation drives out the good because of exactly this sentiment.
Is it really a sentiment, or a fact? If you want to be strict in what you accept, you have to be ok with rejecting stuff that would work, but isn’t strictly conformant.
You can lament that is the case, but it is just the way it is.
It's valid to choose to use strict standards-conforming software. It's quite arguable that such lenient mail servers are broken in this fashion, since the spec requires a domain (and thus IP addresses are not valid in MX records).
Sorry man but this sounds like a "you" problem. You probably need to fix your mail server or get a new one.