Email to club rejected with "550 Request failed; Mailbox unavailable"

Beginning 12/21/2022, emails that I send to the member email is being rejected. I have tried resending the message the last two days and still receive the message. I've been able to send emails to our members for years. Any idea what may be causing this issue and how to correct it? Thank you!  Mark Kramer, DTM.

Rejection email text, below: Your message did not reach some or all of the intended recipients.      Subject:     TM: A Look Ahead 12/28/2022-01/25/2023      Sent:  12/21/2022 7:04 PMThe following recipient(s) cannot be reached:      'members-457@toastmastersclubs.org' on 12/21/2022 7:04 PM            550 Request failed; Mailbox unavailable 

I don't see any issues with your club address.
Are you sure that you're sending the email from your usual address?  Email to members sent from addresses not registered on your club website will be rejected

Hi Pam;

Thanks for responding. Yes, I'm using the same email address I've used for years to send the emails. In fact, the weekly emails I send to the club as recently as the previous week from the same email address to the same email address, worked fine.

Mark

We are not blocking emails from the advertised IP addresses for mkramer@flash.net,
I suggest you talk to your email service provider.
[000.014]    MX:A-->al-ip4-mx-vip1.prodigy.net144.160.235.143
[000.016]    MX:A-->al-ip4-mx-vip2.prodigy.net144.160.235.144
[000.018]    MX:A-->ff-ip4-mx-vip1.prodigy.net144.160.159.21
[000.020]    MX:A-->ff-ip4-mx-vip2.prodigy.net144.160.159.22

Woodrow Samuel II VC5 has Secondary Email Address truelifemusick@aol.com.

We resolved the issue last night. Apparently, a few of us had been using an outdated distribution list email address that must have been taken down last month. Someone else had the current distribution list email address and we successfully used it.