sub validate_fields {
    ...
    if($q->param(mail)) {
        my $mod =  '/home/tanger/www/mods';
        unshift @INC, $mod
            unless $INC[0] eq $mod;
        require Email::Valid;      # to include the code
        import Email::Valid;       # to import symbols into your namespace
        ...
    }
    ...
}