I fine-tuned the subject field ;)
John C Klensin writes:
Of course, the firm requirement in 2821 that all domains in email
addresses be fully-qualified, plus either a little knowledge or a
quick determination that "hostname" is not a TLD, is sufficient to
reject such messages as non-deliverable as soon as they touch the
mail system and possibly earlier.
But the hostnames I see _are_ fully qualified. Don't you have messages
From: "Something R. Other" <something(_at_)example(_dot_)com>
I have tens of thousands of messages where the From field's domain is a
strict postfix of the Sender field's domain. I don't know how to
estimate how many of the Sender addresses are deliverable, but it's few
enough that I consider them all untrustworthy and don't use them.
The fact that those rejections do not occur often enough may be more
evidence about the futility of trying to fix these sorts of problems
by fine-tuning standards.
I sort of agree with the argument, except that IMO it doesn't apply in
the common case.