Re: Programmers with network engineering skills

[Owen DeLong <owen () delong com>]

I don't believe that is true.

From RFC-821, it is true that:

@ONE, @TWO:JOE@THREE

Is supposed to be valid as a forward path, but, not an address. However,  I believe its
use is effectively, if not actually deprecated at this point.

It doesn't really describe address, per se, but, it does define mailbox as follows:

   mailbox

      A character string (address) which identifies a user to whom mail
      is to be sent.  Mailbox normally consists of the host and user
      specifications.  The standard mailbox naming convention is defined
      to be "user@domain".  Additionally, the "container" in which mail
      is stored.

Looking at more recent RFC 5321,

One important change is this:

   Only resolvable, fully-qualified domain names (FQDNs) are permitted
   when domain names are used in SMTP.  In other words, names that can
   be resolved to MX RRs or address (i.e., A or AAAA) RRs (as discussed
   in Section 5) are permitted, as are CNAME RRs whose targets can be
   resolved, in turn, to MX or address RRs.  Local nicknames or
   unqualified names MUST NOT be used.  There are two exceptions to the
   rule requiring FQDNs:

   o  The domain name given in the EHLO command MUST be either a primary
      host name (a domain name that resolves to an address RR) or, if
      the host has no name, an address literal, as described in
      Section 4.1.3 and discussed further in the EHLO discussion of
      Section 4.1.4.

Regarding addresses, it says this:

2.3.11.  Mailbox and Address

   As used in this specification, an "address" is a character string
   that identifies a user to whom mail will be sent or a location into
   which mail will be deposited.  The term "mailbox" refers to that
   depository.  The two terms are typically used interchangeably unless
   the distinction between the location in which mail is placed (the
   mailbox) and a reference to it (the address) is important.  An
   address normally consists of user and domain specifications.  The
   standard mailbox naming convention is defined to be
   "local-part@domain"; contemporary usage permits a much broader set of
   applications than simple "user names".  Consequently, and due to a
   long history of problems when intermediate hosts have attempted to



Klensin                     Standards Track                    [Page 15]
 
RFC 5321                          SMTP                      October 2008


   optimize transport by modifying them, the local-part MUST be
   interpreted and assigned semantics only by the host specified in the
   domain part of the address.


Yes, there are user parts that are technically valid which my regex would reject. There are also some invalid addresses 
which I don't reject (for example, I won't reject Abc. () example com).

If you want to get truly pathologically pedantic  about it:

http://en.wikipedia.org/wiki/Email_address#Valid_email_addresses

You may have noticed my particular test wouldn't accept foo!bar!ucbvax!user format addresses, either.

It works well enough for my purposes. I did not claim it was perfect.

Owen

On Mar 12, 2012, at 3:01 PM, William Herrin wrote:

> On Mon, Mar 12, 2012 at 5:32 PM, Owen DeLong <owen () delong com> wrote:
> > Whenever I've built code to check someone's email address on a form, I always just looked for the following:
> >
> > 1.      matches ^[^@]+@[A-Za-z0-0\-\.]+[A-Za-z]$
> > 2.      The component to the right of the @ sign returns at least one A, AAAA, or MX record.
>
> Hi Owen,
>
> If I'm not mistaken, "B@M4N"@delong.com is a legitimately formatted
> email address which fails part one of your test. Something along the
> lines of @delong.com;bob@some.private.network is also supposed to be
> legit though it's been so long since I looked at it that I may have
> munged the format.
>
> No, I don't allow these in systems I've designed either. Just sayin'.
>
> Regards,
> Bill Herrin
>
>
>
> -- 
> William D. Herrin ................ herrin () dirtside com  bill () herrin us
> 3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
> Falls Church, VA 22042-3004