E-mail address bounced too many times

We have the following message for the North Adelaide Toastmasters Club:
Emails sent to the primary email address [ (e-mail address) ] for Member (name) have bounced too many times and exceeded the FreeToastHost limit for bounces.

There are three of these for the following active and working e-mails:
alisondo.mydung@gmail.com
vuluc1@gmail.com
samindivara.tm@gmail.com

Can you please fix them? I notice there have been similar posts by other members since the 1st of April.

Also, how are you going with fixing the root cause? I'm a programmer too so happy to help.

Thanks,
Vu

Gmail is seeing the emails as spam, is your club sending emails. with subject "[NATM] Payment Notification"

The Bounce Count for Email Address [alisondo.mydung@gmail.com] has been reset to zero.
The Bounce Count for Email Address [vuluc1@gmail.com] has been reset to zero.
The Bounce Count for Email Address [samindivara.tm@gmail.com] has been reset to zero.

Your email message to alisondo.mydung@gmail.com could not be delivered
and was returned to the FreeToastHost server. Details are as follows:

Recipient Email Address: alisondo.mydung@gmail.com
Email Subject: [NATM] Payment Notification
Date Sent: 1 Jun 2020 15:09:37 +0200

Your email message to vuluc1@gmail.com could not be delivered
and was returned to the FreeToastHost server. Details are as follows:

Recipient Email Address: vuluc1@gmail.com
Email Subject: [NATM] Payment Notification
Date Sent: 1 Jun 2020 15:09:37 +0200

Your email message to samindivara.tm@gmail.com could not be delivered
and was returned to the FreeToastHost server. Details are as follows:

Recipient Email Address: samindivara.tm@gmail.com
Email Subject: [NATM] Payment Notification
Date Sent: 1 Jun 2020 15:09:37 +0200