fix(email): add dns validation of email addresses

packages/api/src/infrastructure/tests/EmailDnsValidationService.test.tsx

@@ -0,0 +1,139 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import {EmailDnsValidationService} from '@fluxer/api/src/infrastructure/EmailDnsValidationService';
+import {describe, expect, test, vi} from 'vitest';
+
+type ResolveMxFn = (domain: string) => Promise<Array<{exchange: string; priority: number}>>;
+type ResolveAddressFn = (domain: string) => Promise<Array<string>>;
+
+interface MockResolver {
+	resolveMx: ReturnType<typeof vi.fn<ResolveMxFn>>;
+	resolve4: ReturnType<typeof vi.fn<ResolveAddressFn>>;
+	resolve6: ReturnType<typeof vi.fn<ResolveAddressFn>>;
+}
+
+function createDnsError(code: string): Error & {code: string} {
+	const error = new Error(`DNS lookup failed: ${code}`) as Error & {code: string};
+	error.code = code;
+	return error;
+}
+
+function createMockResolver(): MockResolver {
+	return {
+		resolveMx: vi.fn<ResolveMxFn>(),
+		resolve4: vi.fn<ResolveAddressFn>(),
+		resolve6: vi.fn<ResolveAddressFn>(),
+	};
+}
+
+describe('EmailDnsValidationService', () => {
+	test('accepts email domains that have MX records', async () => {
+		const resolver = createMockResolver();
+		resolver.resolveMx.mockResolvedValue([{exchange: 'mx.example.com', priority: 10}]);
+		const service = new EmailDnsValidationService({
+			resolver,
+			enforceInTestMode: true,
+		});
+
+		const result = await service.hasValidDnsRecords('person@example.com');
+
+		expect(result).toBe(true);
+		expect(resolver.resolveMx).toHaveBeenCalledWith('example.com');
+		expect(resolver.resolve4).not.toHaveBeenCalled();
+		expect(resolver.resolve6).not.toHaveBeenCalled();
+	});
+
+	test('falls back to A/AAAA when MX is missing', async () => {
+		const resolver = createMockResolver();
+		resolver.resolveMx.mockRejectedValue(createDnsError('ENODATA'));
+		resolver.resolve4.mockResolvedValue(['192.0.2.10']);
+		resolver.resolve6.mockResolvedValue([]);
+		const service = new EmailDnsValidationService({
+			resolver,
+			enforceInTestMode: true,
+		});
+
+		const result = await service.hasValidDnsRecords('person@example.com');
+
+		expect(result).toBe(true);
+		expect(resolver.resolveMx).toHaveBeenCalledWith('example.com');
+		expect(resolver.resolve4).toHaveBeenCalledWith('example.com');
+		expect(resolver.resolve6).toHaveBeenCalledWith('example.com');
+	});
+
+	test('rejects domains that have no MX and no A/AAAA records', async () => {
+		const resolver = createMockResolver();
+		resolver.resolveMx.mockRejectedValue(createDnsError('ENODATA'));
+		resolver.resolve4.mockRejectedValue(createDnsError('ENODATA'));
+		resolver.resolve6.mockRejectedValue(createDnsError('ENODATA'));
+		const service = new EmailDnsValidationService({
+			resolver,
+			enforceInTestMode: true,
+		});
+
+		const result = await service.hasValidDnsRecords('person@example.com');
+
+		expect(result).toBe(false);
+	});
+
+	test('rejects domains that do not exist', async () => {
+		const resolver = createMockResolver();
+		resolver.resolveMx.mockRejectedValue(createDnsError('ENOTFOUND'));
+		const service = new EmailDnsValidationService({
+			resolver,
+			enforceInTestMode: true,
+		});
+
+		const result = await service.hasValidDnsRecords('person@missing-domain.invalid');
+
+		expect(result).toBe(false);
+		expect(resolver.resolve4).not.toHaveBeenCalled();
+		expect(resolver.resolve6).not.toHaveBeenCalled();
+	});
+
+	test('fails open on transient resolver errors', async () => {
+		const resolver = createMockResolver();
+		resolver.resolveMx.mockRejectedValue(createDnsError('ETIMEOUT'));
+		const service = new EmailDnsValidationService({
+			resolver,
+			enforceInTestMode: true,
+		});
+
+		const result = await service.hasValidDnsRecords('person@example.com');
+
+		expect(result).toBe(true);
+	});
+
+	test('caches results by normalised domain', async () => {
+		const resolver = createMockResolver();
+		resolver.resolveMx.mockResolvedValue([{exchange: 'mx.example.com', priority: 10}]);
+		const service = new EmailDnsValidationService({
+			resolver,
+			enforceInTestMode: true,
+		});
+
+		const first = await service.hasValidDnsRecords('person@Example.com');
+		const second = await service.hasValidDnsRecords('someone@example.com');
+
+		expect(first).toBe(true);
+		expect(second).toBe(true);
+		expect(resolver.resolveMx).toHaveBeenCalledTimes(1);
+	});
+});