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I am facing an old-fashioned setup, where emails are fetched (and deleted) using POP3 from several accounts, and stored in Thunderbird's "local folders", organized in folders and subfolders.

The project is to move all that mess into a single Gmail account, so that everything can be accessed at a single, remote location using IMAP.


Would the migration be as easy as just, in Thunderbird, copying the emails from the local folders to the remote IMAP account, or are there caveats to consider? Would some information be lost/altered in the process?

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    I just drag and drop between local folders, IMAP folders, and Gmail folders in Thunderbird. It seems to work fine.
    – Tim
    Commented Aug 16, 2017 at 19:21
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    I have had issues with creating folder trees in the past, but copying the messages works fine. If your folder structure is not too complicated, you might want to create the folders first, then copy the messages in blocks of ca. 1000
    – Eugen Rieck
    Commented Aug 16, 2017 at 19:57

2 Answers 2

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  1. In Thunderbird, add the Gmail account as IMAP (not POP3, which might be the default option).

  2. Verify the account sync is working.

  3. Create each folder manually, as mentioned above. The folder tree structure is difficult to copy.

  4. Copy items from each folder - blocks of up to 5000 messages worked fine for me

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I had a similar problem when around last month I decided to ditch Thunderbird. Now perhaps (hopefully) drag'n'drop or copy-pasting will work for you (and if it does, there is nothing wrong with it), but for me and my thousands of mails, these procedures didn't get me far: usually, after 15-500 mails, Thunderbird simply dropped the connection. After ruling out the option of copying each message independently (and then checking if it really got copied), I looked around in the internet and found

this Python script simply named "IMAP Upload".

Please note that I am neither gaining profits from suggesting this nor am I the developer of this tool.

Although it seems that the tool isn't maintained any longer, it still worked well (after fiddling around quite a lot - see below).

My workflow:

  • Saving everything from the IMAP-account locally (and temporarily shifting it in separate (sub)folders) - This is just a precaution: That way, in the case of failure, your nicely sorted inbox won't get messed up.
  • Just using Thunderbird's Profile-structure for exporting the POP-account failed miserably, so I ended up using ImportExportTools to export every (sub)folder separately (maybe a bit paranoid; but for me, exporting them all together didn't work)
  • Then, I'd run python imap_upload.py --gmail --box=<ENTER_FOLDER_NAME> [email protected] --password=password --retry=10 <THUNDERBIRD_PROFILE_FOLDER>/Profiles/<YOUR_PROFILE>/Mail/<POP-ACCOUNT>/<FOLDER_EXPORT_NAME>.sbd (of course, you have to fill in everything inside < > and your username and password. ;-) )
    • It's best to check if the --box-value was accepted after each upload (For me, 2/35 were not properly created and the mails ended up in the main inbox, though I cannot rule out typos or mistakes on my side).

As to your question regarding lost information: the dates were not altered and I still have every attachment, every Umlaut and every Smiley in my mails. That is to say: My randomly handpicked comparisons (and some tools) say so.

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