Need to parse a variable to see if it contains more than 1 email address

I have a perl / cgi script that allows a web site visitor to send the page they are on to another persons email address... "refer to a friend".

The problem is that a spammer has targeted this process, and has made a process that submits many many email addresses to the cgi program, and is using my form, and a comment field (for the spam message) to send out his spam and abuse my network.

The "to" address is contained in the variable: $FORM_DATA{"to"}

I am wanting a perl snippit that I would place in a subroutine before mailing, that would test this address, and if there was more than one email address in the field, it would return an error to the screen and stop the cgi execution.

I would like the code for an answer to be in subroutine format (working code), and if the code you suggest works as I paste it in the program, then you get the points. Post your email-at-domain if you want me to send you the entire script.

Thanks!

(I would be interested in expanding the points to exclude a person from using the form more than 1x per day, by logging IP address, but that is not as critical as the above.)
rapidhostAsked:
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rkosaiCommented:
To check if a variable contains more than one email address, we can check for invalid address characters. Because those characters would 1)serve as delimiters, or 2)be invalid anyways, we can use this code:

sub valid_email {
  my $email = shift;
  if ($email =~ /[^\w\@\.]/) {return 0} else {return 1};
}

You could use it like this:

my $addr = $FORM_DATA{"to"};
if (valid_email($addr)) {
  #send mail
} else {
  #display error message
}
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ozoCommented:
Except that there are no characters that are invalid in email addresses.
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rkosaiCommented:
There are actually a few invalid characters in an email address.  Space, newlines, carriage returns, and many of the symbols (such as $, #, %, etc) are not allowed in email addresses.  In addition, commas tend to be used as delimiters so they also can't be used.
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ozoCommented:
$ # % etc are allowed in email addresses, and Space, newlines and carriage returns may be used when in quotes.  Commas also need to be quoted
http://www.faqs.org/rfcs/rfc822.html
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