Exchange issue: Remote Server returned '500 5.3.3 Unrecognized command'

Hello, I have been having this issue for some time now and cant seem to narrow it down. We have one vendor we cant email. Everytime I lookup the error it states their server does not have sufficient disk space. I have redacted our server info. I cant seem to figure out where the error is coming from because they keep telling me their server has sufficient space. I also performed a couple of MX tests and their server seems to fail the TLS tests.

remote.TFSJax.com rejected your message to the following email addresses:
'rreyes@tfsjax.com' (rreyes@tfsjax.com)
The recipient's email system can't process this message. Please try resending the message later.
remote.TFSJax.com gave this error:
Unrecognized command

Diagnostic information for administrators:
Generating server: "my mail server"
rreyes@tfsjax.com
remote.TFSJax.com
Remote Server returned '500 5.3.3 Unrecognized command'
Original message headers:
Received: from "my mail server" by
 "my mail server" with Microsoft SMTP Server
 (TLS) id 15.0.1263.5; Fri, 29 Dec 2017 10:12:40 -0500
Received: from "my mail server" by
 "my mail server" with Microsoft SMTP Server
 (TLS) id 15.0.1263.5; Fri, 29 Dec 2017 10:12:39 -0500
Received: from "my mail server" ([fe80::b8bb:d61a:d661:452]) by
 "my mail server"([fe80::b8bb:d61a:d661:452%12]) with mapi id
 15.00.1263.000; Fri, 29 Dec 2017 10:12:39 -0500
From: "me:
To: "'rreyes@tfsjax.com'" <rreyes@tfsjax.com>
Subject: Test
Thread-Topic: Test
Thread-Index: AdOAt3TkYICXtvZZRzORQP6KJ/1sFQ==
Date: Fri, 29 Dec 2017 15:12:39 +0000
Message-ID: <cb403fd5fab544589c51c3e9e587e522@"my email server">
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach:
X-MS-TNEF-Correlator:
x-ms-exchange-transport-fromentityheader: Hosted
x-originating-ip: [xxx.xxx.xxx.xxx]
Content-Type: multipart/alternative;
      boundary="_000_cb403fd5fab544589c51c3e9e587e522S"myemailserver_"
MIME-Version: 1.0
Return-Path: "my email"


DNS RESULTS:
Reply from 96.94.55.86: bytes=32 time=21ms TTL=58
Reply from 96.94.55.86: bytes=32 time=15ms TTL=58
Reply from 96.94.55.86: bytes=32 time=14ms TTL=58
Reply from 96.94.55.86: bytes=32 time=14ms TTL=58

Ping statistics for 96.94.55.86:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 14ms, Maximum = 21ms, Average = 16ms

C:\Users\administrator.CO>nslookup remote.TFSJax.com
Server:  "my dns server"
Address:  xxx.xxx.xxx.xxx

Non-authoritative answer:
Name:    remote.TFSJax.com
Address:  96.94.55.86


C:\Users\administrator.CO>nslookup tfsjax.com
Server:  "my dns server"
Address:  xxx.xxx.xxx.xxx

Non-authoritative answer:
Name:    tfsjax.com
Address:  96.94.55.86


C:\Users\administrator.CO>nslookup 96.94.5.86
Server:  "my dns server"
Address:  xxx.xxx.xxx.xxx

Name:    96-94-5-86-static.hfc.comcastbusiness.net
Address:  96.94.5.86
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