#!/usr/bin/perl
 
SUB check_email {
    # Initialize local email variable with input to subroutine.              #
    $email = $_[0];
 
    # If the e-mail address contains:                                        #
    IF ($email =~ /(@.*@)|(\.\.)|(@\.)|(\.@)|(^\.)/ ||
 
        # the e-mail address contains an invalid syntax.  Or, if the         #
        # syntax does not match the following regular expression pattern     #
        # it fails basic syntax verification.                                #
 
        $email !~ /^.+\@(\[?)[a-zA-Z0-9\-\.]+\.([a-zA-Z]{2,3}|[0-9]{1,3})(\]?)$/) {
 
        # Basic syntax requires:  one or more characters before the @ sign,  #
        # followed by an optional '[', then any number of letters, numbers,  #
        # dashes or periods (valid domain/IP characters) ending in a period  #
        # and then 2 or 3 letters (for domain suffixes) or 1 to 3 numbers    #
        # (for IP addresses).  An ending bracket is also allowed as it is    #
        # valid syntax to have an email address like: user@[255.255.255.0]   #
 
        # Return a false value, since the e-mail address did not pass valid  #
        # syntax.                                                            #
        RETURN 0;
    }
 
    ELSE {
 
        # Return a true value, e-mail verification passed.                   #
        RETURN 1;
    }
}