Once a week or so, a reader writes in to ask how to back up his or her Yahoo! Mail account.

I've covered this issue before (three long years ago!) but apparently I didn't cover all the bases -- particularly regarding how to back up mail that's not in your Yahoo! inbox; that is, mail that you have archived in folders on the Yahoo! Mail service.

After some back and forth with reader Joe Sokol, I realized it's probably time to outline the entire backup system from start to finish, with a particular emphasis on backing up those online folders full of mail.

So here we go!

First, and most importantly, this will only work if you have a Yahoo! Mail Plus account, which is $19.99 a year. There are tools to download your email from Yahoo! Mail without one of these accounts, but I've never tried them and can't recommend them one way or another.

With Yahoo! Mail Plus set up, you need an offline mail-reading client. Microsoft Outlook will work, or try Thunderbird if you want a free solution.

Next, configure the software to access your Yahoo! Mail account using these instructions and settings. You'll find detailed instructions for virtually every mail client under the "Accessing Yahoo! Mail via POP" drop-down. IMPORTANT: Remember that if you want to leave your mail on the Yahoo! Mail server so you can access it online, set the client to "Leave messages on server" (or similar) during setup. If you skip this step, your mail client will download all the mail and delete it from the web service.

Once you set this up and download your messages, you'll first get all the email from your inbox -- but messages you have put into folders won't be downloaded.

If you want to grab these messages, follow these simple steps (these steps assume you're leaving messages on the Yahoo! Mail server; if not, you can ignore any instructions to move files back into their Yahoo! Mail folders since they'll be deleted as you download them).

> In your offline client, create a new folder (call it "temp inbox") and put all the mail you already downloaded into it.

> In your offline client, create folders to mimic the structure of each folder you have on Yahoo! Mail.

> In Yahoo! Mail, create a "temp inbox" folder and drop all the mail currently in the inbox into it. Both your offline client and Yahoo! Mail inbox should be empty now.

> Open the first folder you have in Yahoo! Mail. Move all the mail there into your inbox. Click the "Send/Receive" button in your offline client. This will download all the mail that's now in the inbox.

> When finished, move all the mail now in your offline client inbox into the corresponding folder you just created. Go back to Yahoo! Mail and move all the messages back into the folder you took them from. Both inboxes should once again be empty.

> Repeat the previous two steps for each folder in your Yahoo! Mail account until you've gone through all the folders and downloaded all the messages. Move the email from the "temp inbox" folders back to the inbox, and you're done! Going forward, all email received in your Yahoo! Mail inbox will be downloaded to your offline client -- but only if you download it before moving it into another folder on Yahoo! Mail.

Once you have your mail in Outlook, you can back it up if you want to copy it to another hard drive or other archiving medium. The instructions from my earlier post explain how to do that.

Got more Yahoo! Mail backup questions? I hope not... but drop me a line if you do!