I am an Ubuntu member and have an @ubuntu.com email address. I want to use this address to reply to mails from using Thunderbird.
Right now this email address is mapped my one of my email-id on Google Apps. I tried adding my account on thunderbird
Since I do not know the password, I left it and went ahead and met a dead end
Anyone has been successful in adding that email ID. I have the actual email added in Thunderbird to which this email id maps to. Do I need to modify that?
You can create a dummy @ubuntu.com account in Thunderbird and configure it so that it uses your gmail SMTP settings. What you did wrong above is that you tried to set up a IMAP/POP/SMTP server for ubuntu.com, which are not available.
See more at http://chrisjohnston.org/2010/send-ubuntu-email-on-iphone
If you were to use your Web browser to access GMail, there is an option in Settings/Accounts to add the new identity, and therefore send email as @ubuntu.com.
The concept you probably want is a Thunderbird "identity". To add an additional identity (such as a different sender email address), edit the account in the account settings window and click the Manage Identities button -- you may have to drag the window up if you're on a low resolution netbook.
What you can do is set up your email account from say, gmail (If that is the one that the @ubuntu.com email will be sending your mail to...) make sure the account is functioning then go to Tools -> Account Settings -> Email Address -> Put in your @ubuntu.com email. It will be using your gmail to send the mail it'll just look like its coming from the @ubuntu.com one. I do it all the time and it works just fine. Sends/Receives like a champ :)