"Not a Member" Confirmation emails with no provocation

Club #7346209 club members are getting these emails since  yesterday.
Not sure if its attack or bug?
Can some one  confirm on this?

If your members are getting "not a Member" messages. It is their email service that is causing it. Please turn off the administrator option in email security

Hi Brian!

Where would the email security administrator option be found in the ADMIN portal?

1. always put your name and club name and number
2. read the documentation - it's very good information and available 24-7
3. I will give you a hint - it's shown in the documentation under EMAIL SECURITY

1. always put your name and club name and number
    Super Communicators #1098516
2. read the documentation - it's very good information and available 24-7
    Documentationion -- where?? On the Free ToastHost 3 Support and Development Site or on the Club Site in the Admin Console, or somewhere else?
3. I will give you a hint - it's shown in the documentation under EMAIL SECURITY
On the Free ToastHost 3 Support and Development Site, I see in the top nav, How to use FreeToastHost, which has a dropdown box. Nowhere under either 'Documentation Index' or 'Document Listing' sections any mention of EMAIL SECURITY.

I sense some frustration given the 3-point bulleted response, I understand you would really like users to self-service, and I appreciate you are volunteers. I work in digital marketing and know my way around websites, yet I still have no idea where to find the documentation to stop the "Not a Member' email notification messages that are being sent to current club members.

So please, provide a link to where the documentation is, if it's on this support site, or let us know if it's somewhere in the club site's admin console and I will then likely be able to find EMAIL SECURITY to self-service the rest of the way.

Thank you for your patience, time and energy to help us out.
 

Brian wrote:

If your members are getting "not a Member" messages. It is their email service that is causing it. Please turn off the administrator option in email security

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Super Communicators, Club #1098516

Can you explain further what you mean by their "email service is causing it"?  70% of my club members have the same Outlook Exchange business email domain, 20% of club members have gmail.com, and 10% have different Outlook Exchange business email domains. I wonder if this is related to the privacy protection updates with Google, Yahoo, and Outlook ? If so, have sender email domains being used for our Toast Host sites been DKIM authenticated?