From 9eeace6bc2ebd97698d3de6f41b70a87a0ca9a31 Mon Sep 17 00:00:00 2001
From: overthelex <overthelex@users.noreply.github.com>
Date: Thu, 2 Jul 2026 15:23:13 +0300
Subject: [PATCH] feat(email): block RU/SU TLDs + disposable domains in
 validation
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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validateEmail now rejects addresses on RU/SU TLDs, common Russian webmail
(yandex.com, ya.ru, …) and disposable providers (mailinator, yopmail, …)
with reason "blocked", before the MX check. These domains have valid MX so
MX-only validation would let them through; we don't mail them.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 src/utils/email-validate.ts  | 50 ++++++++++++++++++++++++++++++++++--
 tests/email-validate.test.ts | 22 +++++++++++++++-
 2 files changed, 69 insertions(+), 3 deletions(-)

diff --git a/src/utils/email-validate.ts b/src/utils/email-validate.ts
index 33ad1e0..d4840cd 100644
--- a/src/utils/email-validate.ts
+++ b/src/utils/email-validate.ts
@@ -8,6 +8,48 @@ export interface EmailValidation {
 // Reasonable syntax check (not full RFC 5322 — deliberately conservative).
 const SYNTAX_RE = /^[^\s@]+@[^\s@.]+(\.[^\s@.]+)+$/;
 
+// TLDs we never mail (RU/SU — not a target audience, hurts sending reputation).
+const BLOCKED_TLDS = [".ru", ".su"];
+
+// Exact registrable domains we block: Russian webmail hosted on other TLDs +
+// common disposable/throwaway providers. Matches the domain or any subdomain.
+const BLOCKED_DOMAINS = new Set<string>([
+  // Russian webmail (mail.ru/list.ru/bk.ru/inbox.ru are already .ru)
+  "yandex.com",
+  "yandex.by",
+  "yandex.kz",
+  "ya.ru",
+  // Disposable / throwaway (curated subset of the most common)
+  "mailinator.com",
+  "guerrillamail.com",
+  "guerrillamailblock.com",
+  "sharklasers.com",
+  "10minutemail.com",
+  "temp-mail.org",
+  "tempmail.com",
+  "throwawaymail.com",
+  "yopmail.com",
+  "getnada.com",
+  "dispostable.com",
+  "maildrop.cc",
+  "fakeinbox.com",
+  "trashmail.com",
+  "mailnesia.com",
+  "mohmal.com",
+  "emailondeck.com",
+  "spam4.me",
+]);
+
+function isBlockedDomain(domain: string): boolean {
+  if (BLOCKED_TLDS.some((tld) => domain.endsWith(tld))) return true;
+  if (BLOCKED_DOMAINS.has(domain)) return true;
+  // Subdomain of a blocked domain (e.g. foo.mailinator.com)
+  for (const d of BLOCKED_DOMAINS) {
+    if (domain.endsWith("." + d)) return true;
+  }
+  return false;
+}
+
 // Per-domain MX cache — registry data repeats domains heavily, so one lookup
 // per domain saves tens of thousands of DNS queries on a 60k import.
 const mxCache = new Map<string, boolean>();
@@ -30,12 +72,16 @@ async function domainHasMx(domain: string): Promise<boolean> {
   return ok;
 }
 
-// Full check: syntax + the domain actually has mail exchangers.
-// This is what cuts the bounce rate on stale registry addresses.
+export { isBlockedDomain };
+
+// Full check: syntax → domain blocklist (RU/SU + disposable) → MX records.
+// This is what cuts the bounce rate on stale registry addresses and keeps us
+// off domains we should never mail.
 export async function validateEmail(email: string): Promise<EmailValidation> {
   const addr = email.trim().toLowerCase();
   if (!validateSyntax(addr)) return { valid: false, reason: "syntax" };
   const domain = addr.slice(addr.lastIndexOf("@") + 1);
+  if (isBlockedDomain(domain)) return { valid: false, reason: "blocked" };
   if (!(await domainHasMx(domain))) return { valid: false, reason: "no_mx" };
   return { valid: true };
 }
diff --git a/tests/email-validate.test.ts b/tests/email-validate.test.ts
index 9990c0c..094188a 100644
--- a/tests/email-validate.test.ts
+++ b/tests/email-validate.test.ts
@@ -1,5 +1,5 @@
 import { describe, it, expect } from "vitest";
-import { validateSyntax } from "../src/utils/email-validate.js";
+import { validateSyntax, isBlockedDomain } from "../src/utils/email-validate.js";
 
 describe("email syntax validation", () => {
   it("accepts normal addresses", () => {
@@ -13,3 +13,23 @@ describe("email syntax validation", () => {
     }
   });
 });
+
+describe("domain blocklist", () => {
+  it("blocks RU/SU TLDs", () => {
+    for (const d of ["mail.ru", "list.ru", "bk.ru", "example.su", "foo.mail.ru"]) {
+      expect(isBlockedDomain(d)).toBe(true);
+    }
+  });
+
+  it("blocks RU webmail on other TLDs and disposable providers", () => {
+    for (const d of ["yandex.com", "ya.ru", "mailinator.com", "yopmail.com", "sub.mailinator.com"]) {
+      expect(isBlockedDomain(d)).toBe(true);
+    }
+  });
+
+  it("allows normal domains", () => {
+    for (const d of ["gmail.com", "ukr.net", "i.ua", "meta.ua", "law.com.ua"]) {
+      expect(isBlockedDomain(d)).toBe(false);
+    }
+  });
+});