// domain part.
	if _, ok := domainToReverseLabels(in); !ok {
		return mailbox, false
	}

	mailbox.local = string(localPartBytes)
	mailbox.domain = in
	return mailbox, true
}

// domainToReverseLabels converts a textual domain name like foo.example.com to
// the list of labels in reverse order, e.g. ["com", "example", "foo"].
func domainToReverseLabels(domain string) (reverseLabels []string, ok bool) {

			}
			uri, err := url.Parse(uriStr)
			if err != nil {
				return fmt.Errorf("x509: cannot parse URI %q: %s", uriStr, err)
			}
			if len(uri.Host) > 0 {
				if _, ok := domainToReverseLabels(uri.Host); !ok {
					return fmt.Errorf("x509: cannot parse URI %q: invalid domain", uriStr)
				}
			}
			uris = append(uris, uri)
		case nameTypeIP:
			switch len(data) {