When you forward bcc to the contacts, do you put your own address in the To: box?

I have just encountered this same issue with the past day (since 3.23.22).

Prior to this issue, I would send a group message, but the BCC box for the recipients; This allowed for suppressing the showing of all email addresses to the recipients. I never had any issues sending an email this way.

Within the past day, when I attempt to send a message to multiple recipients using the BCC field, I get this error message: "The message could not be sent using Outgoing server (SMTP) smtp.mail.yahoo.com for an unknown reason. Please verify that your Outgoing server (SMTP) settings are correct and try again."

I have not touched these settings. I have sent test emails without triggering this error message.

sfhowes asks whether the sender has included their email address in the "To: Box"

I have never done this because I am one of the BCC recipients

Some providers might reject messages that are all bcc, so it's recommended to enter your address in the To: box, even if you are on the bcc list.

Check that the authentication method on Yahoo accounts is OAuth2.

What worked in the past is not guaranteed to work in the present.