After a few moments this is the error message I get twice when I open Thunderbird 3., after it has downloaded my e mails. I am using 7 home premium. I am wondering whether it is the settings on two of my accounts (I have a total of 3). The server settings for my main account are Server name: mail.plus.net Username: surname, and the Account name is name @surname.pus.com. For one of the other accounts the Account name is firstname.lastname@example.org and the Server name is surname.plus.com and the Username is user. It seems to send and receive e mails fine.
You've set up the email account wrong, you shouldn't be trying to connect to surname.plus.com, you should be trying to connect to either mail.plus.net or relay.plus.net to receive and send, respectively. Remove and re-create the email account as per our setup guides