Not many people use nutscrape 7 so there probably aren't many who can help although your question is clear to me
I myself am not sure how netscape works, presumably the email client is seperate to the browser??
I suspect it isn't prompting for the password because it is saved.
How would you normally compose a new message? Can you reply to a message you receive? If not, when you try and send it what error message do you get?