Unnecessary email throttling rejections

I have an employee who uses a Comcast email account to communicate with our business.  I recently added his email to our outage notification system, and Comcast's servers replied with: 

Could not deliver message to the following recipient(s):

Failed Recipient: redacted@comcast.net
Reason: Remote host said: 421 4.2.0 174.136.78.66 Throttled - try again later. Please see https://postmaster.comcast.net/smtp-error-codes.php#RL000003

   -- The header and top 20 lines of the message follows --

Received: from smtp.mydomain.com (NNN-N-NN-NNN-Jacksonville.hfc.comcastbusiness.net [NNN-N-NN-NNN]) by sending_server.domain.net with SMTP
 (version=TLS\Tls12
 cipher=Aes256 bits=256);
   Thu, 15 Oct 2026 12:04:16 -0400
dkim-signature: v=1; a=rsa-sha256; d=mydomain.com; s=secure;
 c=relaxed/relaxed; q=dns/txt; h=From:Subject:Date:Message-ID:To:MIME-Version:Content-Type:Content-Transfer-Encoding;
 bh=F2VJmmeZxaCirm2G4+3OggbsaXu7ztC1fCWkMxR6VWg=;
 b=X28C1MPTBnfC2aKGgV/cyuScgONR5rT3KfKo1JwIP9O6yduPTvnljfQtBAT75T+6EosaDZ4HYXqQInMWwfq+YAkVLzu06No7JB7MtQ1K3lkEkVN4THiYVvKAmDI9UXnVjQHo2qJDTwkkKspGRka2QOS+hwJaeig2DMkc9A9jHui5cFZTQUBw3y4+EAX929d8pGf71gr2HuhD0CbLh+xRgixKWZfZJIWl7CxQxfQ1L2QJLXHRT+79MhYBwN
 0I18NrSz0hPqwWW2tmeuXP8lrI1X39CjPMjiMewe6ynEMEmXwvhkomTPV74sVaxNim153NH68OAlq00PNNTRnySEe7qA==
Received: from pfSense.localdomain (pfSense.localdomain [192.168.100.NNN])
 by smtp.mydomain.com with ESMTPA
 ; Thu, 15 Oct 2026 12:04:09 -0400
From: notify@mydomain.com
To: monit-alerts@mydomain.com
Subject: pfSense WAN DNS -- Connection succeeded WAN_189_DNS
Date: Thu, 15 Oct 2026 16:04:16 GMT
X-Mailer: Monit 5.29.0
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
Message-Id: <1792080256.a7e6253a39c792f@pfSense.localdomain>

Connection succeeded Service WAN_189_DNS 

 Date:        Thu, 15 Oct 2026 12:04:15
 Action:      alert
 Host:        pfSense.localdomain
 Description: connection succeeded to [1.1.1.1]:53 [UDP/IP]

Your faithful employee,
Monit

These messages inform him that our Comcast business Internet service is either down or up, and are intelligently managed by custom notification code hosted on a smart firewall system.  They represent probes of our 5 static IPs.  When Comcast's connectivity fails, the notifier will send out one message for each connectivity failure, back to back.  When connectivity returns, it send out one message per connectivity success.  Preferably, it send out no messages meaning the our Comcast Business Internet is stable and reliable.  However, this is the real world, and outages do happen.  I am operating using a validated Internet email server hosted both inside the Comcast network (on a Comcast owned IP assigned to my business) and redundantly via an external email server that received forwarded messages that are sent via a domain that has a valid inclusive SPF record.  The messages are DKIM signed and valid, not in any way UCE or SPAM.  How do I get Comcast to whitelist the IP addresses associated with the actual notification server and verified forwarding server?

user_82f56f - [Edited: "Personal Information”] 

[Edited: "Personal Information”]  <--- primary email address