diff --git a/lib/index.js b/lib/index.js
index 7bd7b9a..7a081d6 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -36,6 +36,19 @@ const isMultilineGreet = smtpReply => {
   return smtpReply && /^(250|220)-/.test(smtpReply);
 };
 
+/**
+ * @param  {String}  smtpReply A message from the SMTP server.
+ * @return {Boolean}           True if over quota.
+ */
+const isOverQuota = smtpReply => {
+  if (
+    smtpReply &&
+    /(over quota)/ig.test(smtpReply)
+  ) return true;
+
+  return false;
+};
+
 class EmailValidator {
   constructor(options = { }) {
     this.options = Object.assign({
@@ -139,10 +152,15 @@ class EmailValidator {
         log.debug('Mailbox: got data', data);
 
         if (isInvalidMailboxError(data)) return ret(false);
+
+        if (isOverQuota(data)) return ret(false);
+        
         if (!data.includes(220) && !data.includes(250)) return ret(null);
 
         if (isMultilineGreet(data)) return;
 
+        
+
         if (messages.length > 0) {
           const message = messages.shift();
           log.debug('Mailbox: writing message', message);
diff --git a/test/index.js b/test/index.js
index c7a9fbd..a9c0e94 100644
--- a/test/index.js
+++ b/test/index.js
@@ -230,6 +230,24 @@ describe('lib/index', () => {
         return self.validator.verify('bar@foo.com')
           .then(({ validMailbox }) => should(validMailbox).equal(null));
       });
+
+
+      it('returns false on over quota check', () => {
+        const msg = '452-4.2.2 The email account that you tried to reach is over quota. Please direct';
+        const socket = new net.Socket({ });
+
+        self.sandbox.stub(socket, 'write').callsFake(function(data) {
+          if (!data.includes('QUIT')) this.emit('data', msg);
+        });
+
+        self.connectStub.returns(socket); 
+
+        setTimeout(() => socket.write('250 Foo'), 10);
+
+        return self.validator.verify('bar@foo.com')
+          .then(({ validMailbox }) => should(validMailbox).equal(false));
+      });
+
     });
 
     context('given no mx records', () => {