Emails continue to being delayed-receive bounce back/warning message

Thought Employee Michelle had resolved the problem with emails being delayed/bounce-back warning message received, but it happened again yesterday.  Please help!  I'm about to lose my biggest client if this doesn't get resolved.
  See below for copy of email:
This message was created automatically by mail delivery software.
A message that you sent has not yet been delivered to one or more of its
recipients after more than 4 hours on the queue on bosmailout10.eigbox.net.

The message identifier is:     1isxEn-0008Q3-OZ
The date of the message is:    Sat, 18 Jan 2020 18:10:38 -0500
The subject of the message is: LUCE - Spectrum account closed 1/18/20 - Jan 18, 2020

The addresses to which the message has not yet been delivered are:

  darbyjones@professionalfiduciary.com
    host mx1.emailsrvr.com [184.106.54.1]
  carolsmith@professionalfiduciary.com
    host mx1.emailsrvr.com [184.106.54.1]
    Delay reason: SMTP error from remote mail server after RCPT TO:<carolsmith@professionalfiduciary.com>:
    451 4.7.1 Received too many messages from a new or untrusted IP:
    66.96.188.10 (Z27/33FF698) (G28)

No action is required on your part. Delivery attempts will continue for
some time, and this warning may be repeated at intervals if the message
remains undelivered. Eventually the mail delivery software will give up,
and when that happens, the message will be returned to you.


Reporting-MTA: dns; bosmailout10.eigbox.net

Action: delayed
Final-Recipient: rfc822;darbyjones@professionalfiduciary.com
Status: 4.0.0
Remote-MTA: dns; mx1.emailsrvr.com

Action: delayed
Final-Recipient: rfc822;carolsmith@professionalfiduciary.com
Status: 4.0.0
Remote-MTA: dns; mx1.emailsrvr.com
Diagnostic-Code: smtp; 451 4.7.1 Received too many messages from a new or untrusted IP: 66.96.188.10 (Z27/33FF698) (G28)


Return-path: <leann@astresslesstransition.com>
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    id 1isxEn-0008Q3-OZ; Sat, 18 Jan 2020 18:10:41 -0500
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Received: from 072-186-205-030.res.spectrum.com ([72.186.205.30])
 by emailmg.homestead.com
 with HTTP (HTTP/1.1 POST); Sat, 18 Jan 2020 18:10:38 -0500
MIME-Version: 1.0
Content-Type: multipart/mixed;
 boundary="=_d7118104b1273e7cde576eb0cc31ff2c"
Date: Sat, 18 Jan 2020 18:10:38 -0500
From: Leann Moore - A Stress-Less Transition LLC
 <leann@astresslesstransition.com>
To: Carol Smith <carolsmith@professionalfiduciary.com>, Darby Jones
 <darbyjones@professionalfiduciary.com>
Subject: LUCE - Spectrum account closed 1/18/20 - Jan 18, 2020
Organization: A Stress-Less Transition, LLC
In-Reply-To: <4C69B3F7-7AE9-44B4-A41B-7A71826B35B3@aol.com>
References: <4C69B3F7-7AE9-44B4-A41B-7A71826B35B3.ref@aol.com>
 <4C69B3F7-7AE9-44B4-A41B-7A71826B35B3@aol.com>
Message-ID: <1e1d8a238d15a0455d3727916529cbef@astresslesstransition.com>
X-Sender: leann@astresslesstransition.com
User-Agent: Roundcube Webmail/1.3.8
X-EN-AuthUser: leann@astresslesstransition.com
Sender:  Leann Moore - A Stress-Less Transition LLC
 <leann@astresslesstransition.com>


X-EN-Class: impinc