type rfc2821Mailbox struct {
	local, domain string
}

// parseRFC2821Mailbox parses an email address into local and domain parts,
// based on the ABNF for a “Mailbox” from RFC 2821. According to RFC 5280,
// Section 4.2.1.6 that's correct for an rfc822Name from a certificate: “The
// format of an rfc822Name is a "Mailbox" as defined in RFC 2821, Section 4.1.2”.
func parseRFC2821Mailbox(in string) (mailbox rfc2821Mailbox, ok bool) {
	if len(in) == 0 {

				}

				// If the constraint contains an @ then
				// it specifies an exact mailbox name.
				if strings.Contains(constraint, "@") {
					if _, ok := parseRFC2821Mailbox(constraint); !ok {
						return nil, nil, nil, nil, fmt.Errorf("x509: failed to parse rfc822Name constraint %q", constraint)
					}
				} else {
					// Otherwise it's a domain name.
					domain := constraint

	{"******@****.***", "_somename", "example.com"},
}

func TestRFC2821Parsing(t *testing.T) {
	for i, test := range rfc2821Tests {
		mailbox, ok := parseRFC2821Mailbox(test.in)
		expectedFailure := len(test.localPart) == 0 && len(test.domain) == 0

		if ok && expectedFailure {
			t.Errorf("#%d: %q unexpectedly parsed as (%q, %q)", i, test.in, mailbox.local, mailbox.domain)