Thunderbird sending emails from old account

Well this is an odd one. I dropped an old (really old - dial up) email account from my windows PC earlier this year (they shut it down). Converted (Yay) to Ubuntu a couple of months ago, set up thunderbird on install with only the new (googlemail) address. Everything in all the settings / account settings etc show ONLY the googlemail email address (I'm using IMAP not POP).

I've just discovered that as of about 03 September 2010, all my outgoing emails have been sent in the name of the old redundant email address (which no longer exists).

Checked all the account settings, I can only see the googlemail settings.

So. I'm stumped. Help ?

Please ?