[whatwg] Comments on the definition of a valid e-mail address
Brian.P.Campbell at dartmouth.edu
Mon Aug 24 13:33:41 PDT 2009
On Aug 24, 2009, at 3:24 PM, Aryeh Gregor wrote:
>> Yup. If it is deliverable then surely it's an alias to the same
>> without the trailing dot, in which case a browser could choose to
> Yes, it's not possible for "example.com." to mean anything different
> from "example.com". (In fact they do mean something different in DNS,
> but "example.com." means the same thing as what "example.com" is
> normally used to mean. Moreover, the meaning of "example.com" in DNS
> is basically nonsense for web apps processing user-submitted e-mail
> addresses. At least, as far as I understand it; I don't know too much
> about DNS.)
Actually, the trailing dot is meaningful. A domain without a trailing
dot is a relative domain; for example, if you are within the
"example.com" domain, then "foo" could resolve to
"foo.example.com" (or if that doesn't exist, then it would try
resolving that at the root level, and fail since "foo" is not a TLD).
A domain with a trailing dot is an absolute domain; it will only ever
be resolved at the root level.
This difference may be significant. If someone manages to register the
top level domain "mail" (which may be possible if the proposed new
gTLD rules are passed), and has an email address of "foo at mail", then
you might want to distinguish between that resolving to "foo at mail.wikimedia.org
" vs. "foo at mail."
Of course, this is complicated because the trailing dot is technically
not allowed in an email address, but it seems to work in some contexts
that I've tried (though most just strip off the trailing dot).
About the more general subject of this thread, I have tested sending
myself email at all of the following addresses, all of which seem to
work just fine, though some generate warnings in my mail client (Apple
Brian P. Campbell at dartmouth.edu
...brian...p...campbell... at dartmouth.edu
brian.p.campbell at dartmouth.edu.
Brian (this is a test) P (of comments) Campbell (and whitespace)@(here
comes the domain) dartmouth.edu
brian p campbell
Note that Dartmouth has a very permissive email system that allows
name components to be delimited by whitespace and/or periods, and
prefixes of name components as long as you wind up with a unique
match. And of course the address without the domain only works when
I'm sending within the same domain. In some cases, the addresses were
altered slightly in the process of being sent, for example 'Brian P. Campbell at dartmouth.edu
' came through as '"Brian P. Campbell"@dartmouth.edu'.
Given that there are so many technically invalid addresses that
actually do work to deliver mail, and that I'm sure some people have
odd addresses due to poor form validation (perhaps someone has signed
up for an email account on a web form and it allowed spaces in the
address), it's probably best to be relatively lenient about the
addresses allowed. I think the best you can do is look for at least
one character, followed by an @ sign, followed by a legal domain name
(which seems to be more strictly checked, though given the presence of
IDNs, may not be easy to restrict in the future as well).
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