diff --git a/application/config.js b/application/config.js
new file mode 100644
index 0000000..c061895
--- /dev/null
+++ b/application/config.js
@@ -0,0 +1,48 @@
+// Note: Also update app.json and README.md!
+
+const config = {
+	email: {
+		domains: process.env.DOMAINS,
+		deleteMailsOlderThanDays: process.env.DELETE_MAILS_OLDER_THAN_DAYS
+	},
+	imap: {
+		user: process.env.IMAP_USER,
+		password: process.env.IMAP_PASSWORD,
+		host: process.env.IMAP_SERVER,
+		port: 993,
+		tls: true,
+		authTimeout: 3000,
+		refreshIntervalSeconds: process.env.IMAP_REFRESH_INTERVAL_SECONDS
+	},
+	http: {port: normalizePort(process.env.PORT || '3000')}
+}
+
+if (!config.imap.user || !config.imap.password || !config.imap.host) {
+	throw new Error('IMAP is not configured. Use IMAP_* ENV vars.')
+}
+
+if (!config.email.domains) {
+	throw new Error('DOMAINS is not configured. Use ENV vars.')
+}
+
+/**
+ * Normalize a port into a number, string, or false.
+ */
+
+function normalizePort(val) {
+	const port = parseInt(val, 10)
+
+	if (isNaN(port)) {
+		// Named pipe
+		return val
+	}
+
+	if (port >= 0) {
+		// Port number
+		return port
+	}
+
+	return false
+}
+
+module.exports = config