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

xxx@aol.com
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 (67.195.228.84) 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 (10.10.14.12) by
 exchange.mydomain.org (10.10.14.12) 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-MS-Has-Attach:
X-MS-TNEF-Correlator:
x-originating-ip: [10.10.90.20]
Content-Type: multipart/alternative;
   boundary="_000_7ec64c1667be421a827e25eb27d46d78mydomain.com_"
MIME-Version: 1.0