Numeric domain names in user email addresses - bug

Michael Allan mike at
Sat Aug 28 20:34:35 EDT 2010

Thomas von der Elbe wrote:
> Ok, if an email-adress like thx at is somehow wrong lets
> disallow it. I didnt quite understand the text you linked to. Why do
> wrong emailadresses exist at all?

I guess the short answer is that the mail host administrator made a
mistake (maybe a calculated one).  He chose a non-standard domain
name.  There's probably no way to prevent that, because the Internet
is multi-layered and general purpose.  Near the bottom layers, the
domain name system imposes almost no restrictions on name syntax:

RFC 2181 says that almost any name is valid *as* a domain name.  But
that doesn't mean it's OK for a mail host.  Paragraph 3 says:

  Note however, that the various applications that make use of DNS
  data can have restrictions imposed on what particular values are
  acceptable in their environment.  For example, that any binary label
  can have an MX record does not imply that any binary name [""
  or ""] can be used as the host part of an e-mail address.

Standard practices for naming mail hosts are here:

  The labels ["gmx", "de", "1138", "com"] must follow the rules for
  ARPANET host names.  They must start with a letter, end with a
  letter or digit, and have as interior characters only letters,
  digits, and hyphen.  ...

No alarm bells go off if you break the rules.  They're only enforced
ad hoc by the top layer applications (like Votorola) that depend on
them.  So the admin's "mistake" is corrected by rejecting his email

Eventually we'll be able to accept almost any email address, whether
it's standard or not.  But it'll take some work to design the
translation scheme.  And the corresponding wiki usernames (for the
non-standard addresses) won't be quite so short and neat; they'll be
stuffed with encoding characters.

Michael Allan

Toronto, +1 647-436-4521

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