I recently had a problem sending an email from my Talk21 Email address using Thunderbird on a Windows 10 computer. The mail had no links or attachments but seems to have been identified identified as spam, or phishing or malware. The email concerned £10,000 grants that the UK government is giving to small businesses to help them survive the consequences of coronavirus. (I can provide the full text if anyone wants it.) I can see that the subject matter might have resulted in a high score in some scam processing. I wrote and sent the email as normal but Thunderbird produced a pop-up window with this text: An error occurred while sending mail. The mail server responded: We're sorry, but we can't send your email. Either the subject matter, a link, or an attachment potentially contains spam, or phishing or malware. Please check or edit your message and try sending it again. (6-1-3-2) ID (5E3A254B1410CDE9). Please check the message and try again. My email was not received by the recipient even thought it was in Sent Items which I have always assumed confirms successful dispatch of an email. I sent it by BT Yahoo webmail later in the day and this worked. Please can someone who understands these things tell me if it is possible that the email server is saying it will not send the email but that Thunderbird is treating it as sent correctly and so copying it into Sent Items. I think it likely that the BT helpdesk will try to blame Thunderbird for the problem so I would like to know where I stand.