fix(mail): block restricted sender before provider fallback

src/mail.ts

@@ -43,6 +43,19 @@ export class MailError extends Error {
   }
 }
 
+export function assertEmailSenderAllowed(...addresses: string[]): void {
+  const blocked = new Set(
+    (process.env.EMAIL_QUEUE_BLOCKED_SENDERS ?? '')
+      .split(',')
+      .map((address) => address.trim().toLowerCase())
+      .filter(Boolean),
+  );
+  const senders = addresses.map((value) => (/<([^>]+)>/.exec(value)?.[1] ?? value).trim().toLowerCase());
+  if (senders.some((address) => blocked.has(address))) {
+    throw new MailError('Outbound sending from this mailbox is paused for administrator review.');
+  }
+}
+
 // ---------------------------------------------------------------------------
 // Providers
 // ---------------------------------------------------------------------------
@@ -1619,6 +1632,7 @@ export function smtpTransport(account: Account) {
 }
 
 export const sendViaSmtp: SmtpSender = async (account, outgoing) => {
+  assertEmailSenderAllowed(account.email, account.user, outgoing.from);
   const transporter = smtpTransport(account);
   const info = await transporter.sendMail({
     from: outgoing.from,
@@ -1703,6 +1717,7 @@ export async function sendMail(
     isBlocked?: HostBlockCheck;
   } = {},
 ): Promise<SendResult> {
+  assertEmailSenderAllowed(account.email, account.user, outgoing.from);
   const choice = chooseTransport(account, options.resendKey, options.via);
   const smtp = options.smtp ?? sendViaSmtp;
   const resend = options.resend ?? resendSender();

test/mail.test.ts

@@ -631,6 +631,26 @@ describe('sendMail', () => {
     expect(isTransportFailure('550 5.1.1 recipient rejected')).toBe(false);
     expect(isTransportFailure('Resend refused the message: domain is not verified')).toBe(false);
   });
+
+  it('stops a blocked mailbox before SMTP or Resend fallback', async () => {
+    const previous = process.env.EMAIL_QUEUE_BLOCKED_SENDERS;
+    process.env.EMAIL_QUEUE_BLOCKED_SENDERS = 'ettinger@gmail.com';
+    const calls: string[] = [];
+    try {
+      await expect(sendMail(account({ email: 'ettinger@gmail.com', user: 'ettinger@gmail.com' }), {
+        ...outgoing,
+        from: 'Me <ettinger@gmail.com>',
+      }, {
+        resendKey: 'key',
+        smtp: async () => { calls.push('smtp'); return 'must-not-send'; },
+        resend: async () => { calls.push('resend'); return 'must-not-send'; },
+      })).rejects.toThrow(/paused for administrator review/);
+      expect(calls).toEqual([]);
+    } finally {
+      if (previous === undefined) delete process.env.EMAIL_QUEUE_BLOCKED_SENDERS;
+      else process.env.EMAIL_QUEUE_BLOCKED_SENDERS = previous;
+    }
+  });
 });
 
 describe('Resend', () => {