I have had Thunderbird on windows 10 on my laptop some time but I've had this annoying error message on numerous occasions in the past and it can last for two or three days when I can't send any emails at all and then suddenly it's gone and everything works normally again. So the other day I had it again when I tried to send the same message to 8 different recipients. So I knocked off the email address that it said was unavailable and tried again, same error, then did the same again for each recipient and got the same error. Now I know for certain that the email address's are correct, that their mail boxes are not full and are available. So any idea's please.