Yahoo mail bouncing on some messages

Hi All,
I’m trying to help a friend but can’ find the answer. Emails newsletters sent by our synagogue are bouncing. Emails sent by an individual at the synagogue come thru fine. They all end in:
The error is:
From: ShulCloud Mailer <>
Date: Tue, Apr 6, 2021 at 9:31 AM
Subject: Shulcloud Mailer: Bounce Reported - Congregation Kol Emeth
To: <[](mailto:>

An error occurred when attempting to send the email "Memorial Service for Ruth " to

Please check your records and correct or remove the email address from your list.

The receiving mail server returned the below text:

Delivery Report: Array
[UserAgent] =>
[ComplaintFeedback] =>
[FeedbackID] => 01000178a8066554-1a75ce9e-1fd5-4e24-9541-4a51435ed47a-000000
[Status] =>

Strongly suspect your group mailouts from Shulcloud have been designated as spam by various services, possibly by too many coming at too quick a rate. You may be able to set a rate or a number of emails per hour in their settings. Alternatively you could try sending the newsletter emails to groups of 50 or less and see if that helped. I take it that the individual you mention also had a address?

I would also enquire of Shulcloud if they’ve had experience of this.