valid email being rejected by FTH

This is the error message we get when sending an email using members-5750@toastmastersclubs.org

********* was skipped because it has previously bounced too
many times. Please visit support.toastmastersclubs.org and post a
support request message for more information.

I have not posted the email address for privacy reasons but can send it to you if you need it.
I just took over looking after our web site. This has been a problem for over a year now but I am not sure what our previous web person tried. The member who's email is getting blocked or rejected is super frustrated. It is her company email, not sure if that matters.

Please help!

We need the email address if we are going to find out what the issue is.

Here is the message I get when I sign in as admin.
[Wed, 23 Jun 2021 16:18:41 UTC, FreeToastHost System Warning]

Emails sent to the secondary email address [ coachk@nickellsilver.ca ] for Member Kristin Nickells, DTM in Club 5750 have bounced too many times and exceeded the FreeToastHost limit for bounces. The error information for the last bounced email is as follows:

Your email message to coachk@nickellsilver.ca could not be delivered
and was returned to the FreeToastHost server. Details are as follows:

Recipient Email Address: coachk@nickellsilver.ca
Email Subject: [WoD] 6/30/2021 Meeting Notification: Role Change / World of
Date Sent: Wed, 23 Jun 2021 16:18:32 +0000

Diagnostic Code: 550 5.7.1 [CS] Message blocked. If this is a false positive, please report this to your hosting service provider. See console.mailchannels.net/insights/bounce...xid=4299ef493b4702f5
Delivery Status: 5.0.0
Date Last Attempted:
Thanks!

1) As per the message you posted, that host is blocking email from FTH.
They will have to contact their mail host and have the block removed.

2) The Bounce Count for Email Address [coachk@nickellsilver.ca] has been reset to zero. If they do not lift the email block at their host, FTH will issue the block again so we don't get labeled as a spammer.

Okay, I will pass on the message. I have seen in some of the other posts something about adding an email address to the white list? Would this help in her case?

It might, but their host is actively blocking FTH.