feat(email): configurable reply-to address (#3140)

packages/config/src/ConfigLoader.ts

@@ -163,6 +163,7 @@ function defaultConfig(): MasterConfig {
 				provider: 'none',
 				from_email: '',
 				from_name: 'Fluxer',
+				reply_to_email: '',
 				app_base_url: '',
 			},
 			voice: {
@@ -292,6 +293,12 @@ function requireString(value: string | undefined, envName: string): void {
 	}
 }
 
+function validateReplyToEmail(value: string): void {
+	if (value !== '' && !/^[^\s@<>,;"]+@[^\s@<>,;"]+$/.test(value)) {
+		throw new Error('FLUXER_EMAIL_REPLY_TO_EMAIL must be a single email address such as [email protected]');
+	}
+}
+
 function validateUploadRelaySecret(value: string): void {
 	const trimmed = value.trim();
 	if (trimmed.length === 0) {
@@ -566,6 +573,7 @@ function normalizeConfig(config: MasterConfig): MasterConfig {
 	validateStorageChangeFeedConfig(config);
 	validateCachePurgeConfig(config);
 	validateStoreBillingConfig(config);
+	validateReplyToEmail(config.integrations.email.reply_to_email);
 	normalizeAppOriginAliases(config);
 	assertIntegerInRange(config.services.api.max_inflight_requests, 'FLUXER_API_MAX_INFLIGHT_REQUESTS', 1, 100_000);
 	assertIntegerInRange(config.services.api.headers_timeout_ms, 'FLUXER_API_HEADERS_TIMEOUT_MS', 1_000, 3_600_000);

packages/config/src/MasterConfig.ts

@@ -169,6 +169,7 @@ export interface MasterConfig {
 			provider: 'smtp' | 'none';
 			from_email: string;
 			from_name: string;
+			reply_to_email: string;
 			app_base_url: string;
 			webhook_secret?: string;
 			smtp?: {

packages/config/src/__tests__/ConfigLoader.test.ts

@@ -290,6 +290,30 @@ describe('ConfigLoader', () => {
 		expect(config.services.api.storage_change_feed?.skip_buckets).toBeUndefined();
 	});
 
+	test('reads the email reply-to address', async () => {
+		stubMinimalEnv({FLUXER_EMAIL_REPLY_TO_EMAIL: '[email protected]'});
+
+		const config = await loadConfig();
+
+		expect(config.integrations.email.reply_to_email).toBe('[email protected]');
+	});
+
+	test('leaves the email reply-to address empty when unset or blank', async () => {
+		stubMinimalEnv({FLUXER_EMAIL_REPLY_TO_EMAIL: ' '});
+
+		const config = await loadConfig();
+
+		expect(config.integrations.email.reply_to_email).toBe('');
+	});
+
+	test.each(['support', 'Support <[email protected]>', '[email protected],[email protected]', ' [email protected]'])(
+		'rejects %j as the email reply-to address',
+		async (value) => {
+			stubMinimalEnv({FLUXER_EMAIL_REPLY_TO_EMAIL: value});
+			await expect(loadConfig()).rejects.toThrow('FLUXER_EMAIL_REPLY_TO_EMAIL must be a single email address');
+		},
+	);
+
 	test('keeps explicit passkey relying party values', async () => {
 		stubMinimalEnv({
 			FLUXER_BASE_DOMAIN: 'chat.example.com',

packages/config/src/__tests__/EnvironmentOverrides.test.ts

@@ -52,6 +52,7 @@ describe('buildNamedFluxerEnvOverrides', () => {
 			FLUXER_S3_FORCE_PATH_STYLE: 'true',
 			FLUXER_AUTH_BLUESKY_KEYS: '[{"kid":"key-1","private_key_path":"/etc/fluxer/keys/bluesky.pem"}]',
 			FLUXER_STRIPE_PRICE_MONTHLY_USD: 'price_monthly_usd',
+			FLUXER_EMAIL_REPLY_TO_EMAIL: '[email protected]',
 		});
 
 		expect(overrides).toMatchObject({
@@ -62,7 +63,10 @@ describe('buildNamedFluxerEnvOverrides', () => {
 				bluesky: {keys: [{kid: 'key-1', private_key_path: '/etc/fluxer/keys/bluesky.pem'}]},
 			},
 			s3: {force_path_style: true},
-			integrations: {stripe: {prices: {monthly_usd: 'price_monthly_usd'}}},
+			integrations: {
+				stripe: {prices: {monthly_usd: 'price_monthly_usd'}},
+				email: {reply_to_email: '[email protected]'},
+			},
 		});
 	});
 
@@ -77,6 +81,7 @@ describe('buildNamedFluxerEnvOverrides', () => {
 				FLUXER_LIVEKIT_DEFAULT_REGION: blank,
 				FLUXER_AUTH_BLUESKY_KEYS: blank,
 				FLUXER_EMAIL_FROM_NAME: blank,
+				FLUXER_EMAIL_REPLY_TO_EMAIL: blank,
 			}),
 		).toEqual({});
 	});

packages/config/src/config_loader/EnvironmentOverrides.ts

@@ -148,6 +148,7 @@ const NAMED_FLUXER_ENV_OVERRIDES: Record<string, NamedEnvOverride> = {
 	FLUXER_EMAIL_PROVIDER: {path: ['integrations', 'email', 'provider']},
 	FLUXER_EMAIL_FROM_EMAIL: {path: ['integrations', 'email', 'from_email']},
 	FLUXER_EMAIL_FROM_NAME: {path: ['integrations', 'email', 'from_name']},
+	FLUXER_EMAIL_REPLY_TO_EMAIL: {path: ['integrations', 'email', 'reply_to_email']},
 	FLUXER_EMAIL_APP_BASE_URL: {path: ['integrations', 'email', 'app_base_url']},
 	FLUXER_EMAIL_WEBHOOK_SECRET: {path: ['integrations', 'email', 'webhook_secret']},
 	FLUXER_EMAIL_SMTP_HOST: {path: ['integrations', 'email', 'smtp', 'host']},