I am a club secretary and have sent emails to mulitple recipients as BCC on a regular basis. Today this stopped working. I am using Thunderbird Version 128.11.1esr. I updated to this about a week ago. I have not recently updated Windows. The error message says sending the email failed: the subject matter, the attachments or a link may contain spam or phishing or malware. but if I send exactly the same email to one email, to an unblinded address it is sent without problem. I updated Windows today to no effect.