I blogged about Gmail's new feature that helps you migrate from other Web-based e-mail services to Gmail and I have received a lot of e-mails asking if there's a way to back up an offline POP3 e-mail archive to an online e-mail service.
The answer is yes, but depending on what e-mail clients you use, it can require a fair amount of work. If you're using Outlook Express, for example, it's fairly easy. If you use Thunderbird, however, there will be a few extra steps.
First, you will need a Hotmail account, if you don't yet have one; it's free to sign up. After that, download and use Windows Live Mail to connect with the Hotmail account. This process is pretty straightforward.
Windows Live Mail synchronizes with your Hotmail account, which means all the e-mails you have downloaded to your computer will remain on the Hotmail server and be available for you to view using a Web browser.
Apart from Hotmail.com and Live.com e-mail accounts, Windows Live Mail can also handle other types of accounts, including POP3. When you have multiple e-mail accounts with Windows Live Mail, each account will have a separate set of "Inbox," "Sent Items," "Drafts," and so on, as well as other user-created folders.
If you want to upload an existing Outlook Express e-mail archive to your Hotmail account, first run Windows Live Mail and import your Outlook Express messages. (To do this, press Alt-F then choose "Import" on the menu). Once the import process is done, create a new folder within your Hotmail account and name it, say, "POP3 backup." You can create different folders for different groups of e-mails. After that, you can drag and drop or copy messages from the POP3 import into these new folders.
Now all you need to do is sync the Hotmail account and voila! You will see those added folders and e-mails you've just imported on the Hotmail server. This means you can access them wherever you are via a browser and they are saved in Hotmail server.
The sync process can take a long time if you have a big POP3 archive (and a slow connection), and, of course, you can't sync any archive larger than the space allowed by Hotmail, which is 5GB.
If you use Outlook, you can first use Outlook Express to import Outlook's archive before doing the process. Basically, you can use Outlook Express as the intermediary for the import process.
For ThunderBird users, you can use the eml2mbox function of this free conversion tool called IMAPSize to convert Thunderbird's e-mail archive into Outlook Express' format.
Of course, once you have those e-mails in a Hotmail account, you can always import them into Gmail by using the new migration tool. It's good to keep data at multiple places anyway.