How to transfer ALL your e-mail to Gmail (even if it’s in folders)

I recently helped my mother with switching over to Gmail. She has always used the webmail service from our webhost with an e-mail adress at amazoneadvies.nl (she runs a dutch PR consultancy) but the webmail service had been buggy lately. Setting up Gmail to receive e-mail from another account with POP3 access is easy but I was getting worried when I noticed the mail that she had put in folders wasn’t coming through. When I went googling for a clue I found the Gmail answer to this problem:

You’re only receiving mail from the inbox of your other account and not from any folders. Each webmail provider determines which messages to make available for POP download and sends a list of the messages to Gmail. Since Gmail can’t retrieve any messages that aren’t on the list, we suggest contacting your other provider to learn about alternatives.

I didn’t really feel like doing it this way, it meant waiting for our hosting provider to respond and everything. Plus I wasn’t convinced that Gmail would automatically label the messages with the folder name. So I had to come up with another solution.

Gmail allows you to access your e-mail through IMAP which means that you can access your mail with a standard desktop e-mail client like Mozilla Thunderbird. Every change you make in Thunderbird (such as deleting a message) will reflect in your Gmail as well (in contrast to making changes with POP3 access). Our hosting company provides IMAP access as well. What I did was the following:

I turned on IMAP access in Gmail and configured Thunderbird so I could access my mother Gmail (read all about it). Then I created another account in Thunderbird to access her mailbox at our hosting provider (the one the still held some mail in folders). After doing this I could easily create folders for Gmail in Thunderbird (Gmail converts them to labels automatically) that match the folders at our hosting provider. After that I could simply drag and drop all the mail from the hosting provider to Gmail (hold [CTRL] while dragging and dropping to copy instead of move). Voila!

This way all the e-mail that was archived in folders at our hosting provider now appears under matching labels in Gmail.