Hello there jdeboer. We have read your message. We try to help you. Sounds like a server error. servers detected some virus or malware on the e-mails that you are sending. server has detected that your account is sending message to a large number of recipients. You can try to change the account-password. It takes some time like 30 min to check if your email software is available again. And try sending them again. Also you can enable the SMTP authentication on the e-mail client settings to avoid getting banned by the server. After the 30 minutes? Greetings Firefox volunteer.