Bounced email but no prior warning given

Hi
I've just received the following automated warning message, but no prior warning was given that there had been an issue with the email address:

[Mon, 22 Feb 2021 06:25:35 UTC, FreeToastHost System Warning]

Emails sent to the primary email address [ molly.yang5014@yahoo.com.au ] for Guest Molly Yang in Club 7032681 have bounced too many times and exceeded the FreeToastHost limit for bounces.

This automatically generated message is to notify you that this email address ***has been removed*** from the FreeToastHost database to prevent it from causing further bounces. If you are able to resolve the issue with the email address, you will need to re-enter it in the system.

Repeatedly attempting to send emails to invalid, non-working email addresses hurts the overall email reputation of the FreeToastHost system and will not be tolerated.

Please ensure that valid, functioning email addresses are in use to prevent further actions of this nature in the future.

If you have any questions about this warning, please visit support.toastmastersclubs.org and provide us with this message.

I would have made changes earlier if I had known.

Your site admin was given previous notices. The recipient obviously gave you an unused email address.

Your email message to molly.yang5014@yahoo.com.au could not be delivered
and was returned to the FreeToastHost server. Details are as follows:

Recipient Email Address: molly.yang5014@yahoo.com.au
Email Subject: Laugh Out Loud Toastmasters - Wednesday 24th February 2021 at 7:30 pm
Date Sent: Mon, 22 Feb 2021 17:23:10 +1100

Diagnostic Code: 552 1 Requested mail action aborted, mailbox not found
Delivery Status: 5.2.2 mailboxfull
Date Last Attempted: Mon, 22 Feb 2021 06:25:34 GMT