smtp/connection: implement greylist support (#265)

* smtp/connection: implement greylist support

* smtp/connection: use weakmap to track if response has handled greylist

* smtp/connection: fix style nits

* test/client: fix greylist unit

* readme: note greylist support

* smtp/connection: accept code 451 for greylist resend

* smtp/connection: reorder greylist conditionals in response callback

* test/client: only respond once to greylist

README.md

@@ -15,6 +15,7 @@ send emails, html and attachments (files, streams and strings) from node.js to a
 - attachments can be added as strings, streams or file paths
 - supports utf-8 headers and body
 - built-in type declarations
+- automatically handles [greylisting](http://projects.puremagic.com/greylisting/whitepaper.html)
 
 ## REQUIRES
 

smtp/connection.ts

@@ -35,6 +35,7 @@ const SMTP_PORT = 25 as const;
 const SMTP_SSL_PORT = 465 as const;
 const SMTP_TLS_PORT = 587 as const;
 const CRLF = '\r\n' as const;
+const GREYLIST_DELAY = 300 as const;
 
 let DEBUG: 0 | 1 = 0;
 
@@ -115,6 +116,11 @@ export class SMTPConnection extends EventEmitter {
 	protected tls: boolean | SMTPSocketOptions = false;
 	protected port: number;
 
+	private greylistResponseTracker = new WeakMap<
+		(...rest: any[]) => void,
+		boolean
+	>();
+
 	/**
 	 * SMTP class written using python's (2.7) smtplib.py as a base.
 	 *
@@ -393,8 +399,18 @@ export class SMTPConnection extends EventEmitter {
 			if (err) {
 				caller(callback, err);
 			} else {
-				if (codesArray.indexOf(Number(msg.code)) !== -1) {
+				const code = Number(msg.code);
+				if (codesArray.indexOf(code) !== -1) {
 					caller(callback, err, msg.data, msg.message);
+				} else if (
+					(code === 450 || code === 451) &&
+					msg.message.toLowerCase().includes('greylist') &&
+					this.greylistResponseTracker.get(response) === false
+				) {
+					this.greylistResponseTracker.set(response, true);
+					setTimeout(() => {
+						this.send(cmd + CRLF, response);
+					}, GREYLIST_DELAY);
 				} else {
 					const suffix = msg.message ? `: ${msg.message}` : '';
 					const errorMessage = `bad response on command '${
@@ -413,6 +429,7 @@ export class SMTPConnection extends EventEmitter {
 			}
 		};
 
+		this.greylistResponseTracker.set(response, false);
 		this.send(cmd + CRLF, response);
 	}
 

test/client.ts

@@ -213,3 +213,80 @@ test('client constructor throws if `password` supplied without `user`', (t) => {
 			>)
 	);
 });
+
+test.cb('client supports greylisting', (t) => {
+	t.plan(2);
+
+	const msg = {
+		subject: 'this is a test TEXT message from emailjs',
+		from: 'piglet@gmail.com',
+		bcc: 'pooh@gmail.com',
+		text: "It is hard to be brave when you're only a Very Small Animal.",
+	};
+
+	const { onRcptTo } = server;
+	server.onRcptTo = (_address, _session, callback) => {
+		server.onRcptTo = (a, s, cb) => {
+			t.pass();
+			onRcptTo(a, s, cb);
+		};
+
+		const err = new Error('greylist');
+		((err as never) as { responseCode: number }).responseCode = 450;
+		callback(err);
+	};
+
+	client.send(new Message(msg), (err) => {
+		if (err) {
+			t.fail();
+		}
+		t.pass();
+		t.end();
+	});
+});
+
+test.cb('client only responds once to greylisting', (t) => {
+	t.plan(3);
+
+	const msg = {
+		subject: 'this is a test TEXT message from emailjs',
+		from: 'piglet@gmail.com',
+		bcc: 'pooh@gmail.com',
+		text: "It is hard to be brave when you're only a Very Small Animal.",
+	};
+
+	const greylistPort = 2527;
+	const greylistClient = new SMTPClient({
+		port: greylistPort,
+		user: 'pooh',
+		password: 'honey',
+		ssl: true,
+	});
+	const greylistServer = new SMTPServer({
+		secure: true,
+		onRcptTo(_address, _session, callback) {
+			t.pass();
+			const err = new Error('greylist');
+			((err as never) as { responseCode: number }).responseCode = 450;
+			callback(err);
+		},
+		onAuth(auth, _session, callback) {
+			if (auth.username === 'pooh' && auth.password === 'honey') {
+				callback(null, { user: 'pooh' });
+			} else {
+				return callback(new Error('invalid user / pass'));
+			}
+		},
+	});
+
+	greylistServer.listen(greylistPort, () => {
+		greylistClient.send(new Message(msg), (err) => {
+			if (err) {
+				t.pass();
+				t.end();
+			} else {
+				t.fail();
+			}
+		});
+	});
+});