Is root@[127.1] a syntactically valid e-mail address?

Is root@[127.1] a syntactically valid e-mail add开发者_JS百科ress?

Why? Why not?

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You need to check RFC 5322, section 3.4.1.

This specification is a revision of Request For Comments (RFC) 2822, which itself superseded Request For Comments (RFC) 822, "Standard for the Format of ARPA Internet Text Messages", updating it to reflect current practice and incorporating incremental changes that were specified in other RFCs.

I run your email address though http://isemail.info/ that gave the following info:

The general result is: The address is only valid according to the broad definition of RFC 5322. It is otherwise invalid.

The specific diagnosis is: The domain literal is not a valid RFC 5321 address literal

Here is the relevant passage from the email RFCs:

domain-literal = [CFWS] "[" *([FWS] dtext) [FWS] "]" [CFWS]

(RFC 5322 section 3.4.1)

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It depends on whether you mean addresses in the header (RFC 5322) or envelope addresses (RFC 5321), and in the latter case, whether you include <>, everything between <> (i.e. the source route), or just Mailbox.

It's valid according to RFC 5322, but RFC 5322 allows loads of fun things like comments! and unicorns! and cake! and ponies!. It's just about possible to parse them using Perl's "regular" expressions: Mail::RFC822::Address.

It's syntactically invalid according to RFC 5321 Section 4.1.3 since the grammar only allows address literals of the form 1.2.3.4 or with a prefix of the form "standard-tag:" (e.g. [IPv6:::1]). I've assumed you meant "Mailbox", i.e. everything between <> but not including the source route.

I'd use the latter definition, since an e-mail address isn't much good if my SMTP server won't accept it. (Yes, this is a bit of a horrible definition, but I don't think the internet will move away from SMTP any time soon.)

(Additionally, there's RFC 5336 a.k.a. "UTF8SMTP". I'm not aware of anyone who uses this.)

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No, RFC2822 allows IP addresses to be used as domain, but you must use a valid IP address.

Your example should be root@[127.0.0.1].

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According to RFC-822 as you mention in the tags, yes, it is syntactically valid, because the grammar allows it. These are the relevant rules:

 addr-spec   =  local-part "@" domain        ; global address    
 
 domain      =  sub-domain *("." sub-domain)
 
 sub-domain  =  domain-ref / domain-literal

 domain-literal =  "[" *(dtext / quoted-pair) "]"

 dtext       =  <any CHAR excluding "[",     ; => may be folded
                 "]", "\" & CR, & including
                 linear-white-space>

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No,

E-mail validity has some broad definitions, if you split the address into two sections, local (before the @ sign) and domain (after the @ sign). The local part may be alpha-numeric with the following special characters ‘.’, ‘-’ and ‘_’, the local part cannot contain contiguous periods.

The domain part must meet the definition of a host name or ip address surrounded by square braces.

As your example doesn't meet the requirements for a valid host name (foo.bar), and it doesn't contain a valid IP address surrounded by square braces, it is not a valid e-mail address.

Check out the following e-mail validator code (minus the ip address validation bit) which will validate an e-mail address. This can be easily retrofitted to work with ip-address domain names too.