From f25bd69b17bfa141ad3645c0f875b482e8152611 Mon Sep 17 00:00:00 2001
From: denish-fearless <dsubedi@fearless.tech>
Date: Wed, 15 Jan 2025 13:05:25 -0500
Subject: [PATCH] after some research found out that some subdomains do have mx
 records, this will fall back to root domain if subdomain fails

---
 backend/src/middleware/emailValidator.test.ts | 28 +++++++-----------
 backend/src/middleware/emailValidator.ts      | 29 ++++++++++++-------
 2 files changed, 29 insertions(+), 28 deletions(-)

diff --git a/backend/src/middleware/emailValidator.test.ts b/backend/src/middleware/emailValidator.test.ts
index a00a9ca88..03c09db69 100644
--- a/backend/src/middleware/emailValidator.test.ts
+++ b/backend/src/middleware/emailValidator.test.ts
@@ -5,7 +5,7 @@ jest.mock('dns');
 
 const mockedDns = dns as jest.Mocked<typeof dns>;
 
-describe('isValidEmail Function', () => {
+describe('isValidEmail Function (Full and Root Domain Validation)', () => {
 
     afterEach(() => {
         jest.resetAllMocks();
@@ -16,7 +16,7 @@ describe('isValidEmail Function', () => {
         expect(result).toBe(false);
     });
 
-    test('should return true for a valid email with MX records (full domain)', async () => {
+    test('should return true for a valid email with MX records on the full domain', async () => {
         mockedDns.resolveMx.mockImplementation((domain, callback) => {
             if (domain === 'gmail.com') {
                 callback(null, [{ exchange: 'mail.google.com', priority: 10 }]);
@@ -29,14 +29,12 @@ describe('isValidEmail Function', () => {
         expect(result).toBe(true);
     });
 
-    test('should return true for a valid email with MX records (root domain fallback)', async () => {
+    test('should return true for a valid email where MX records exist on the root domain', async () => {
         mockedDns.resolveMx.mockImplementation((domain, callback) => {
             if (domain === 'subdomain.example.com') {
                 callback(null, []);
             } else if (domain === 'example.com') {
                 callback(null, [{ exchange: 'mail.example.com', priority: 20 }]);
-            } else {
-                callback(null, []);
             }
         });
 
@@ -44,7 +42,7 @@ describe('isValidEmail Function', () => {
         expect(result).toBe(true);
     });
 
-    test('should return false for a valid email but no MX records in either domain', async () => {
+    test('should return false when neither the full nor root domain has MX records', async () => {
         mockedDns.resolveMx.mockImplementation((domain, callback) => {
             callback(null, []);
         });
@@ -53,31 +51,25 @@ describe('isValidEmail Function', () => {
         expect(result).toBe(false);
     });
 
-    test('should return false for a domain with an error during MX lookup (full domain)', async () => {
+    test('should return false when an error occurs during full domain lookup and no MX records exist on root', async () => {
         mockedDns.resolveMx.mockImplementation((domain, callback) => {
-            if (domain === 'fakeexample.com') {
+            if (domain === 'subdomain.fakeexample.com') {
                 callback(new Error('Domain not found'), []);
             } else {
                 callback(null, []);
             }
         });
 
-        const result = await isValidEmail('test@fakeexample.com');
+        const result = await isValidEmail('test@subdomain.fakeexample.com');
         expect(result).toBe(false);
     });
 
-    test('should return false for a domain with an error during MX lookup (root domain fallback)', async () => {
+    test('should return false when an error occurs during both full and root domain lookups', async () => {
         mockedDns.resolveMx.mockImplementation((domain, callback) => {
-            if (domain === 'subdomain.fakeexample.com') {
-                callback(new Error('Domain not found'), []);
-            } else if (domain === 'fakeexample.com') {
-                callback(new Error('Domain not found'), []);
-            } else {
-                callback(null, []);
-            }
+            callback(new Error('Domain not found'), []);
         });
 
-        const result = await isValidEmail('test@subdomain.fakeexample.com');
+        const result = await isValidEmail('test@error.com');
         expect(result).toBe(false);
     });
 });
diff --git a/backend/src/middleware/emailValidator.ts b/backend/src/middleware/emailValidator.ts
index 8be86d65d..18e1f16d1 100644
--- a/backend/src/middleware/emailValidator.ts
+++ b/backend/src/middleware/emailValidator.ts
@@ -17,21 +17,30 @@ export const isValidEmail = async (email: string): Promise<boolean> => {
 };
 
 const validateDomainMX = (email: string): Promise<boolean> => {
-    let domain = email.split('@')[1];
-    const domainParts = domain.split('.')
-    if(domainParts.length > 2) {
-        domain = domainParts.slice(-2).join('.')
-    }
+    const domain = email.split('@')[1];
+    const domainParts = domain.split('.');
+    const rootDomain = domainParts.length > 2 ? domainParts.slice(-2).join('.') : domain; // If subdomain exists
+
     return new Promise((resolve) => {
+        // Trying full domain first
         dns.resolveMx(domain, (err, addresses) => {
-            if (err || addresses.length === 0) {
-                console.log(`Invalid domain or no MX records for: ${domain}`);
-                resolve(false);
-            } else {
+            if (!err && addresses.length > 0) {
                 console.log(`Valid MX records found for ${domain}:`, addresses);
-                resolve(true);
+                return resolve(true);
             }
+
+            // Fallback to root domain if the full domain fails
+            dns.resolveMx(rootDomain, (rootErr, rootAddresses) => {
+                if (!rootErr && rootAddresses.length > 0) {
+                    console.log(`Valid MX records found for ${rootDomain}:`, rootAddresses);
+                    resolve(true);
+                } else {
+                    console.log(`Invalid domain or no MX records for: ${domain}`);
+                    resolve(false);
+                }
+            });
         });
     });
 };
 
+