I have been using Thunderbird for quite some time. However a week ago I tried to send an email and it came back as "Login to server smtp.blueyonder.co.uk with username ***************@blueyonder.co.uk failed."
You can also do a quick check on the Spamhaus site directly to see if you have this spambot at https://www.spamhaus.org/query and type in your external IP you can gets this my typing "whats my ip" into google. If you are on the CSSSBL then yes you have a spambot.
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