While working on a complete migration of my previous mail accounts to GMail, (I am honestly one of the last Google Apps users that do not need to pay for the pro version…) I stumbled upon „ImapSync“ (which I refused to use because of the price) and later on, upon „ImapSize“. While ImapSize was able to download all my mails to the handy .mbox format, I wasn´t able to upload my mails to GMail, because of the following error:
„Can´t continue uploading messages: SEARCH completed (Success)“
After testing around and trying to just Copy and Paste the bunch (>20.000) of mails from the old to the new account just by using Outlook, I recognized, that this will not work at all. Outlook just crashed after a couple of minutes. To be clear, this solution will of course work, if you only have a couple of mails to transfer, but I was searching for a general approach with thousands of mails and inboxes sized > 3GB.
So, here is my solution for this problem:
- Download a new version of ImapSize.
- Set Up your old Mail account in ImapSize and press „Crtl“ + „S“ to get the size of your IMAP folders.
- Right click on each of the folder you like to migrate, choosing „Download Messages“, followed by „To mbox (Unix mailbox)“.
- Download and install Thunderbird.
- Set-Up your new (GMail) account in Thunderbird (you can use the auto detection for the servers, based on a well-working ISP look up)
- Open the „Add-ons-Manager“ in Thunderbird and download the „ImportExportTools“. For my migration I used version 126.96.36.199. which was working quite fine.
- Add a new local folder, right click and choose from the new submenu „Import / Export“ the option „Import MBox file“ for each of your saved mail folders
- Just select all mails in the particular local folders and the drag and drop all mails to the IMAP folders. Thunderbird will now spent a lot of time (depending of course on your Internet connection and the amount of mails), synchronizing your mails.