Thunderbird/Email problem

Hi,
I am trying to help a friend with a Mac problem. They have lost all the emails in the email client - Thunderbird. They can still access them through a web client though. It is saying it is off line but whenever I enter the server information it is says the password is incorrect. I have asked my friend that there must be another password but they say there isn't. So I thought I could reset the password but there is no link or help to do this. Being a PC user, I am a bit alien to Mac so hence the post. Sorry if it is a bit vague.

Thanks

It doesn't matter whether you're using a PC or a Mac the procedure is the same. Your friend needs to contact his ISP and reset the password. Once he's able to access the server via the web he should be able to get his email. Of course if his server deletes email after it's downloaded, then it will be gone. However, most servers give the option of retaining the mail after it's downloaded unless the subscriber requests it be removed. And why is he using Thunderbird instead of Apple Mail?