The email client supports pop and imap mailboxes.
I just did a quick google search and it looks like in order to activate pop on your yahoo mail account you have to pay for it. (the same is true of hotmail free version)
Note: the website might be out of date, but i cant help further as I dont use yahoo mail.
For a yearly fee, Yahoo! provides POP access to your Yahoo! Mail account.http://email.about.com/cs/yahoomailtips/qt/et032501.htm
Yahoo! Mail on the Web and on Your Desktop
This means you can use your regular email program (Outlook Express, for example, or Windows Mail, or Mozilla Thunderbird) to receive and send messages with your Yahoo address.
Use Your Email Program with Your Yahoo! Mail Plus Account
After you have signed up for Yahoo! Mail Plus, add a new email account to your email program with the following POP and SMTP settings:
* Yahoo! Mail POP server: plus.pop.mail.yahoo.com
* POP port: 995
* POP TLS/SSL: yes
* POP user name: Your My Yahoo! ID
* Password: Your My Yahoo! password
* Yahoo! Mail SMTP server: plus.smtp.mail.yahoo.com
* SMTP port: 465
* SMTP TLS/SSL: yes
* SMTP user name: Your My Yahoo! ID
* SMTP password: Your My Yahoo! password
If you run into any problems sending or receiving mail with these settings:
* Log in to Yahoo! Mail on the web.
* Select Options | Mail Options.
* Go to the POP & Forwarding category.
* Click View POP Settings for your Yahoo! Mail server settings.
By default, you'll also receive all the spam that goes to the Bulk Mail folder in Yahoo! Mail, but you can prevent downloading this folder via POP.
Access a Free Yahoo! Mail Account in Your Email Program
If you don't want to or can't use the official POP access provided by Yahoo!, YPOPs! can be an alternative, set up easily in Outlook Express, for example, as can be using IzyMail, on any platform and just about any email program.