How To Back Up Yahoo (btinternet) Emails For Free

Introduction

Today I needed to fetch a lot of emails from a friend's yahoo email account and convert them into a text format to be parsed by a script. To do this, I needed to be able to download the emails and make a backup in the process. This tutorial will show you how to do that for free without upgrading your yahoo email account.

Install thunderbird (this is installed by default on Ubuntu, but will have to be manually installed on the likes of Windows)

Create a new email account in thunderbird using the settings specified here (you have to login to get to the linked page)
Incoming mail server settings

POP server: mail.btinternet.com
Use SSL
Port: 995

Outgoing mail server (SMTP) settings

SMTP server: mail.btinternet.com
Use SSL
Port: 465
Use authentication
Account Name/Login Name: Your BT Yahoo! Mail ID (your email address without the "@btinternet.com" domain, for example, "jo.bloggs")
Email Address: Your BT Yahoo! Mail address (for example, "jo.bloggs@btinternet.com")
Password: Your BT Yahoo! Mail password

Download the ImportExportTools addon for thunderbird. Here is a related site describing the addon.

Restart Thunderbird after installing the addon for it to take effect.

Move all the emails you want to backup into a folder, or if you want to backup your entire inbox leave them in there.

Go to tools->ImportExportTools and then click the action you want (probably Export Folder). Then choose the location you want to save to and your done!.