Code to demonstrate promisify any library if they don't return promises.

promisify.js

var client = inbox.createConnection(config);
client.on('connect', function () {
	client.openMailbox('INBOX', function (err, info) {
		if (err) {
			console.error('Box open error', err);
		} else {
			console.log('Message count in INBOX : ' + info.count);
			client.listMessages(0, 1, function (err, messages) {
				if (err) {
					console.error('Message Listing error', err);
					client.close();
				} else {
					//read messages
					client.close();
				}
			});
		}
	});
});
client.on('error', function (err) {
	console.error('Connection error', err);
});
client.connect();


///////////////////////////////////////////////////////////////////////



async function listMessages(client){
	return new Promise((resolve, reject) => {
		client.listMessages(0, 1, function (err, messages) {
			if (err) {
				reject(err);
			} else {
				resolve(messages);
			}
		});
	});
}

async function openMailbox(client){
	return new Promise((resolve, reject) => {
		client.openMailbox('INBOX', function (err, info) {
			if (err) {
				reject(err);
			} else {
				resolve(info);
			}
		});
	});
}

async function ClientConnect(client){
	return new Promise((resolve, reject) => {
		client.on('connect', function () {
			resolve();
		});
		client.on('error', function (err) {
			reject(err);
		});
		client.connect();
	});
}


async function main() {
	try {
		var client = inbox.createConnection(config);
		await ClientConnect(client);
		const info = await openMailbox(client);
		if ( info.count > 0 ) {
			const messages = await listMessages(client);
		} else {
			//log
		}
		client.close();
	} catch (err) {
		console.error(err);
	}
}
main();