On Thu, Feb 09, 2012 at 01:15:52PM +0530, Ram wrote:
> I am trying to validate email ids of subscribers coming to my site
> Is there a standard regular expression for email id syntax that
> confirms to rfc822.
>
> I want to avoid junk entries from entering my database.
>
> Postfix already checks this syntax in RCPT-TO , but is this regex
> available already
Often it is a mistake to attempt to parse complex grammars with mere
regular expressions, some constructs are not handled by regexps in
full generality.
https://tools.ietf.org/html/rfc5322#section-3.4.1
In this case you need to support:
addr-spec = local-part "@" domain
local-part = dot-atom / quoted-string / obs-local-part
domain = dot-atom / domain-literal / obs-domain
domain-literal = [CFWS] "[" *([FWS] dtext) [FWS] "]" [CFWS]
dtext = %d33-90 / ; Printable US-ASCII
%d94-126 / ; characters not including
obs-dtext ; "[", "]", or "\"
So, ignoring obsolete forms, you need a regexp for a valid
quoted-string, and a valid dot-atom. Then:
(<quoted-string-regexp>|<dot-atom-regexp>)@<dot-atom-regexp>
One may be more strict about the domain part, and check it is a valid
DNS domain, and has MX records or A (or AAAA) records. The dot-atom
and quoted-string syntax is defined in other sections of RFCs 5322/5321.
