Hello,

What determines a valid (or invalid) email address? I'm writing a script which can determine whether the formatting is correct or not. For example, you need an "@" sign, a ".", etc. You can't have spaces or backslashes in an email, etc.

Does someone have a complete list of rules?

Thanks,
Steve

Most java scripts that are written to check for a valid e-mail only check for the "@" and that it contains a "." that's it ;)

From the CGI/Perl CookBook:


sub email_check {
local($email) = $_[0];

# Check that the email address doesn't have 2 @ signs, a .., a @., a
# .@ or begin or end with a .

if ($email =~ /(@.*@)|(\.\.)|(@\.)|(\.@)|(^\.)|(\.$)/ ||

# Allow anything before the @, but only letters numbers, dashes and
# periods after it. Also check to make sure the address ends in 2 or
# three letters after a period and allow for it to be enclosed in []
# such as [164.104.50.1]

($email !~ /^.+\@localhost$/ &&
$email !~ /^.+\@\[?(\w|[-.])+\.[a-zA-Z]{2,3}|[0-9]{1,3}\]?$/)) {
return(0);
}

# If it passed the above test, it is valid.

else {
return(1);
}
}

Here's some more Perl code:


$a = "john\@example.com";
print &CheckEmailAddress($a);
sub CheckEmailAddress() {
# This regexp validates the format of an email address. It returns the cleaned
# version of the email address, or blank if the address was not valid.
#
# An email address must be of the form:
# 1) (trim any spaces or tabs or linefeeds or carriage returns)
# 2) (possibly one quotation mark)
# 3) (one or more characters for username, excepting a quotation mark)
# 4) (possibly one quotation mark)
# 5) @
# 6) (one or more characters for hostname(s), excepting [ <>\t])
# 7) .
# 8) (two or more characters for top-level-domain, excepting [ <>\t])
# 9) (trim any spaces or tabs or linefeeds or carriage returns)
#
# 1 2 3 4 56 7 8 9
# .............'''.......'''.'''''''''..'''''''''''' ''''''.............
$_[0] =~ /[ |\t|\r|\n]*\"?([^\"]+\"?@[^ <>\t]+\.[^ <>\t][^ <>\t]+)[ |\t|\r|\n]*/;
return $1;
}

Or, if you're using Perl you can use the module Mail::RFC822::Address.

Or, if you like reading specs, it's supposed to be in RFC822, http://www.faqs.org/rfcs/rfc822.html, but I couldn't find it.

-Z