Avatar of Dan
Flag for United States of America asked on

Exchange not able to send some emails: NDR 550 5.4.300

Hello, my company is having issues sending emails to @aol.com and @yahoo.com

I made sure we're not listed on any spammer lists, I have an SPF and DMARC setup in my external DNS.   Below is the NDR that I got back.

I tried to send an email to xxx@aol.com, and this is what was returned to me.

Any idea's what is wrong?

Delivery has failed to these recipients or groups: xxx@aol.com (xxx@aol.com)
Several attempts to deliver your message were unsuccessful and we stopped trying.
It could be a temporary situation. Try to send your message again later.

Diagnostic information for administrators:
Generating server: exchange.mydomain.org
Receiving server: exchange.mydomain.org
Total retry attempts: 193

12/16/2021 5:01:16 PM - Server at exchange.mydomain.org returned '550 5.4.300 Message expired -> 451 4.4.395 Target host responded with error. -> 421 4.4.1 Connection timed out'
12/16/2021 8:48:58 AM - Server at mx-aol.mail.gm0.yahoodns.net ( returned '451 4.4.395 Target host responded with error. -> 421 4.4.1 Connection timed out'
Original message headers:
Received: from exchange.mydomain.org ( by
 exchange.mydomain.org ( with Microsoft SMTP Server
 (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id
 15.2.922.13; Tue, 14 Dec 2021 09:11:25 -0800
Received: from exchange.mydomain.org ([::1]) by exchange.mydomain.org
 ([::1]) with mapi id 15.02.0922.013; Tue, 14 Dec 2021 09:11:25 -0800
From: Dan <me@mydomain.com>
To: "xxx@aol.com" <xxx@aol.com>
Subject: test 2
Thread-Topic: test 2
Thread-Index: AdfxDZLutegXFZ+wSNGmejtShJ8m5A==
Date: Tue, 14 Dec 2021 17:11:24 +0000
Message-ID: <7ec64c1667be421a827e25eb27d46d78@mydomain.com>
Accept-Language: en-US
Content-Language: en-US
x-originating-ip: []
Content-Type: multipart/alternative;
MIME-Version: 1.0

ExchangeDNSMicrosoftEmail ServersEmail Clients

Avatar of undefined
Last Comment

8/22/2022 - Mon

Log in or sign up to see answer
Become an EE member today7-DAY FREE TRIAL
Members can start a 7-Day Free trial then enjoy unlimited access to the platform
Sign up - Free for 7 days
Learn why we charge membership fees
We get it - no one likes a content blocker. Take one extra minute and find out why we block content.
Not exactly the question you had in mind?
Sign up for an EE membership and get your own personalized solution. With an EE membership, you can ask unlimited troubleshooting, research, or opinion questions.
ask a question

thanks for the quick reply. i updated the reverse PTR yesterday, and my ISP said it could take up to 24 hours to take effect.  today, I'm able to send emails to that domain.

I'll follow the first article you mentioned as soon as I get a chance, I'm out of the office now.
I started with Experts Exchange in 2004 and it's been a mainstay of my professional computing life since. It helped me launch a career as a programmer / Oracle data analyst
William Peck