Email Address Validation Code

This page exists because I've found that nobody in the world puts any effort into writing/maintaining code to validate email addresses. The problem seems fairly simple --- just to figure out if a text string is an email address, or if it's something else freakish that needs to be corrected.

With great sorrow, I must indicate that in all my dealings on the web, that far too many web sites get email address validation terribly wrong. The result is that many people with perfectly valid email addresses, or power users who rely on special address variations to filter their mail must suffer as second class net citizens.

The purpose of this page is to be a repository of free, working code that people can take and use in their environments for address parsing and validation, and information relating to the "field".

Contact me at cache atsymbol cs.cmu.edu to add additional entries to this page.

Important Reading

• RFC2822 Describes the valid email address formats

Common Problems

• The one that gets me most frequently is that the local-part (the username/id) of the address is allowed to contain all sorts of special non-alphabetic and non-numeric characters. Many email systems let you include a '+' symbol to tag messages for special processing by the recipient. Thus, mail sent to 'name+tag@site.com' will get delivered to 'name@site.com', but the recipient can automatically filter it into their mailboxes, forward it to other accounts, or manage personal mailing lists.

Code Snippets

Perl

This code handles non-obsolete address-bits without comments and without random (though legal) whitespace. is_valid_local_email_part takes the stuff before the '@' and tells you if it is valid. is_valid_email will validate an entire email address (Thanks to Bill Entwistle for pointing out a bug).

    sub is_valid_local_email_part ($) { 
        my ($addr) = @_;
        my $atext = qr/[A-Za-z0-9\!\#\$\%\&\'\*\+\-\/\=\?\^\_\`\{\|\}\~]/;
        my $dot_atom_text = qr/$atext+(\.$atext+)*/;

        my $no_ws_ctl_char = qr/[\x01-\x08\x0b\x0c\x0e-\x1f\x7f]/;
        my $qtext_char = qr/([\x21\x23-\x5b\x5d-\x7e]|$no_ws_ctl_char)/;
        my $text = qr/[\x01-\x09\x0b\x0c\x0e-\x7f]/;
        my $qtext = qr/($qtext_char|\\$text)*/;
        my $quoted_string = qr/"$qtext"/;

        if ( $addr =~ /^($dot_atom_text|$quoted_string)$/ ) { 
                return 1;
        } else {
                return 0;
        }
    }
    sub is_valid_email ($) { 
        my ($addr) = @_;
        my $atext = qr/[A-Za-z0-9\!\#\$\%\&\'\*\+\-\/\=\?\^\_\`\{\|\+\~]/;
        my $dot_atom_text = qr/$atext+(\.$atext+)*/;

        my $no_ws_ctl_char = qr/[\x01-\x08\x0b\x0c\x0e-\x1f\x7f]/;
        my $qtext_char = qr/([\x21\x23-\x5b\x5d-\x7e]|$no_ws_ctl_char)/;
        my $text = qr/[\x01-\x09\x0b\x0c\x0e-\x7f]/;
        my $qtext = qr/($qtext_char|\\$text)*/;
        my $quoted_string = qr/"$qtext"/;

        my $quotedpair = qr/\\$text/;
        my $dtext = qr/[\x21-\x5a\x5e-\x7e\x01-\x08\x0b\x0c\x0e-\x1f\x7f]/;
        my $dcontent = qr/($dtext|$quotedpair)/;        
        my $domain_literal = qr/\[(${dcontent})*\]/;

        if ( $addr =~ /^($dot_atom_text|$quoted_string)\@($dot_atom_text|$domain_literal)$/ ) { 
                return 1;
        } else {
                return 0;
        }
    }

Special Thanks

• Chris Myers, who pointed out two mistakes in my regexps
• May 2007, James J Marshall, who pointed out a typo in atext