policy: Implement recipient domain policy for #51

- INBUCKET_SMTP_DEFAULTACCEPT
- INBUCKET_SMTP_ACCEPTDOMAINS
- INBUCKET_SMTP_REJECTDOMAINS

pkg/server/smtp/handler.go

@@ -329,6 +329,11 @@ func (s *Session) mailHandler(cmd string, arg string) {
 			s.logger.Warn().Msgf("Bad address as RCPT arg: %q, %s", addr, err)
 			return
 		}
+		if !recip.ShouldAccept() {
+			s.logger.Warn().Str("addr", addr).Msg("Rejecting recipient")
+			s.send("550 Relay not permitted")
+			return
+		}
 		if len(s.recipients) >= s.config.MaxRecipients {
 			s.logger.Warn().Msgf("Maximum limit of %v recipients reached",
 				s.config.MaxRecipients)

pkg/server/smtp/handler_test.go

@@ -169,6 +169,7 @@ func TestMailState(t *testing.T) {
 		{"RCPT TO:<u1@gmail.com>", 250},
 		{"RCPT TO: <u2@gmail.com>", 250},
 		{"RCPT TO:u3@gmail.com", 250},
+		{"RCPT TO:u3@deny.com", 550},
 		{"RCPT TO: u4@gmail.com", 250},
 		{"RSET", 250},
 		{"MAIL FROM:<john@gmail.com>", 250},
@@ -366,9 +367,11 @@ func setupSMTPServer(ds storage.Store) (s *Server, buf *bytes.Buffer, teardown f
 		Domain:          "inbucket.local",
 		DomainNoStore:   "bitbucket.local",
 		MaxRecipients:   5,
-		Timeout:         5,
 		MaxMessageBytes: 5000,
 		StoreMessages:   true,
+		DefaultAccept:   true,
+		RejectDomains:   []string{"deny.com"},
+		Timeout:         5,
 	}
 
 	// Capture log output