Thunderbird email login problem

[#1]

I am setting up my wife`s new Dell laptop, and using the latest download of Thunderbird as email client.... Laptop is running W7 64 bit.
So far, I have managed to complete the initial setup, and have received mail on her computer, addressed to her, as would be expected....
however, when I try to send an email to my email address, to my laptop, I get a message

Quote

Login to server relay.plus.net failed

how do I rectify this problem, as the password is accepted to release the mail FROM the server mail.plus.net..... why is it not accepting the password for relay.plus.net?

[#2]

Because you've used the wrong username/password?
For outgoing mail, if you are connected to the Plusnet network you don't actually need a username/password. Otherwise it has to be the main account username and password (not username+mailbox).

[#3]

OK... thanks... found the answer...
Thunderbird Toolbar > Account settings > scroll down to > Outgoing Server (SMTP) > Highlight the description > click on Edit > change the user name to ....... (my username) ..