I am migrating all my email to a new server. I have about 10 accounts in 10 different folders in Mozilla Thunderbird. I have been using pop3 in the past, but on the new server I want to use imap.

I have created all the imap accounts on the new server and I want to copy over all the emails on their folders on Thunderbird to their corresponding imap account folders on the new server.

When searching for an answer for this, most people suggest just copying all the emails in their folder to the imap account inbox. Some people say that you should only copy around 500 emails at a time. The problem is I have around 20,000 emails per account (going back to the year 2002!) and Thunderbird just gives up on me. I have managed to get it working occassionally by copying 500 emails at a time but this is going to take forever!

Thunderbird shows that it is copying the emails with a message in the status bar, but after a short while the status message goes blank.

My question is, is there a way of moving a large number of emails from a local folder on Thunderbird to an imap account that works and is quick?

  • Just make sure that the folder is properly indexed by forcing a reindex. I have never had trouble moving thousands of emails after that. Jun 10, 2011 at 11:27
  • Excuse my ignorance but how do you force an index? Is this the same or different from compact folders? I find it frustrating that Thunderbird doesn't have a more complete status window of what it's doing.
    – iagdotme
    Jun 10, 2011 at 13:25
  • Depending on the version of Thunderbird, there should be reindex, or fix option in the folder options (properties, or directly in context menu). Jun 10, 2011 at 13:37
  • 3
    Sadly, Thunderbird sometimes stops copying for no obvious reason ("status message goes blank"), so it might be advisable to compare the number of original emails with the number of total emails in the new folder after the job has completed (otherwise you'd probably lose emails). (Yes, this q is 4 yrs old, but Tb still shows this buggy behavior.)
    – basic6
    Sep 4, 2015 at 11:12

4 Answers 4


I have used Thunderbird to move large quantities of messages from Local to imap. You'll need to ensure that your local folders are indexed properly, and then start with smallish chunks and keep adding more until you get to a comfortable number. The last time I did this I started with about 1000, then 2500, then 5000, and pretty soon I was done. It could take some time, but be patient and try to leave thunderbird alone to do it's work while moving.

  • 1
    Thanks, I've compacted the folders and used the Expunge plug in. I'm copying over 1000 messages at the moment. Just 27,000 to go, and this is only one 1 of my 10 accounts. I was really hoping for a quicker and easier option. However, if this is the only way, then I'll have to try. I'll post back here to let you know how I have got on.
    – iagdotme
    Jun 10, 2011 at 14:27
  • Aggh, it really is so slow. I started with 1000 messages which copied over (slowly) and now Thunderbird has copied over 2000 out of the 5000. Only got 20,000 ish to go for this account. Surely there is a better way?!
    – iagdotme
    Jun 10, 2011 at 17:01
  • 1
    I will really depend upon what the server supports. If you had IMAP'd all of those e-mails, then there is a tool called imapsync which is handy for moving from one imap account to another (So I guess you could build an IMAP server on your local machine, and drag everything in as you8 are doing now, and then imapsync from your local server to the remote one, but that seems like a lot of work.) Some mail servers will support importing messages in MBOX or MAILDIR format, but the ability to import will vary by server.
    – Kirk
    Jun 10, 2011 at 18:00
  • Does your new IMAP account have a webmail interface? If so, there might be import options in there.
    – Kirk
    Jun 10, 2011 at 18:01
  • 1
    However, I have to say the process is much more effective now that I took your advice and indexed/compacted folders. This has certainly helped Thunderbird from giving up!
    – iagdotme
    Jun 10, 2011 at 22:49

Get the add-on named Copy Folder. Then go to Tools > Add Ons, then search "copy folder" and follow prompts. After restarting Thunderbird you simply right-click the folder and it will now give the option of Copy.

  • 4
    It doesn't work well when you have thousands of messages per folder Jan 6, 2015 at 10:11
  • 1
    This did do the bulk of the job for me (creating folders and moving most of the 11,000+ emails), but it does seem buggy. I checked a few folder's email count totals, and not everything made it over. In my case 14 of 45 folders were missing between 1-3 emails each. Sometimes I think it was because there was an email with the same subject and/or sender but different timestamp, but sometimes it just seemed completely random. That said, I had to compare the folders where the counts were off and copy the missing ones manually, which was frustrating.
    – kevinmicke
    Oct 12, 2015 at 17:51

Copying messages via clients like Thunderbird is not reliable for thousands of messages. Instead, I recommend Larch (https://github.com/rgrove/larch). I've used it myself and it works just fine.

  • 1
    Larch cannot copy email from local folders to IMAP servers. In other words, it doesn't do what OP asked. Jul 13, 2017 at 21:19

Yesterday I used this app to copy an entire account into a new folder of a different account. The message flags remain intact, and the folders are created automatically.

When you're done, go to subscribe and turn any folder's checkbox off and then back on, and Thunderbird will refresh your folders list.


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