Incremental e-mail backups with Thunderbird

The Mozilla Thunderbird e-mail client doesn’t provide a back-up tool. It is possible though to use the search function to select only those e-mail messages that are more recent than your last back-up and save them, but this process doesn’t store the folder structure that your messages were in. This is only a working solution if you use only a few folders or none at all. I recently had to restore from a hard disk crash and spent half a day putting e-mails back in folders. (Another option would have been to keep my restored back-up in in its own folder; after all, it’s mostly old mail.)

Looking for back-up tools for Thunderbird, the official recommendation appears to be to get a program called MozBackup. The advantage of MozBackup is that it creates back-ups of profiles for several Mozilla tools, not just Thunderbird. Unfortunately it doesn’t do incremental back-ups.

Looking through’s support forums I encounter mostly disbelief that anybody would want to do incremental back-ups of e-mail messages and folders. As a web developer I often get sent large files by clients and designers. Lately this has decreased a lot—people store their files in the cloud and send me a link—but it still happens. Before the crash I had about 10 GB in e-mail on my hard disk.

There is a back-up plugin (I believe Mozilla uses the word add-on instead of plug-in) called ImportExport Tools which I think I used before to migrate from Pegasus to Thunderbird but which you can also use for back-ups. (Strangely the plug-in is stored under Miscellaneous at instead of Import/Export.) This contains an option for structured storage, that is to say, storing mails with their respective folders. Unfortunately this option won’t let you select the specific mails you want to export, it only works for all mail at once. It does have an automatic back-up setting which may or may not store the folder structure. I will update this posting once I find out more.

Note also that the author of the plug-in reports that storing folders is at the moment unstable, i.e. may not work.

Back-ups are dangerous if you don’t test whether or not you are able to restore them. As far as the ImportExport Tools plug-in is concerned I can report success in this regard. I created a second account in Thunderbird and imported the back-up of my primary account there. I only performed spot checks, I did not check if all mails were recovered.

Another option would be to store e-mail without attachments. That way I could easily store every mail I ever received on a single CD-R, which would make the whole incremental back-up thing just a little less important. Of course you’d have to find a way to store your attachments first. In case you are using your e-mail client as a sort of document management system this won’t work. Let’s say you receive lots of photos of loved ones via e-mail and then when you want to see these photos again later you view them in your mail client. In this example you never bothered to store your attachments in a separate location, so back-ups without attachments would be less of an option.

Storing messages via Search

  1. Empty the Trash folder and any other temporary folders.
  2. Right-click the top-most folder that contains all the messages you wish to export.
  3. In the context menu that pops up, select the item that will let you search messages.
  4. In the search dialog, check the box for searching sub-folders.
  5. In the search dialog, construct the following filter: ‘must’ – ‘date’ – ‘starting’ (these may not be the literal terms, I am working from the Dutch version). Note: you can also use an ‘age in days’ filter.
  6. Click the ‘apply search’ button (again, this is probably named differently).
  7. If you have results, perform a quick check to see they are all you want and no more than you want.
  8. Click the ‘save as search folder’ button, or whatever it is called.
  9. The previous action stores your search results as if it were a mail folder. Close the search dialog, go to the folder you just created and select the messages.
  10. Right click and select Save As.
  11. Make sure you save your messages in a fresh folder on your hard disk if there are many of them.

All your message will now be stored as .eml files in the folder you created. Thunderbird is capable of reading these. Under MS Windows you can even drag and drop them to a folder in Thunderbird.

Storing messages via Import/Export Tools

Since there are several methods for this I will skip the how-to, at least for now. The automated back-up settings are in the plug-in’s Options dialog in their own tab. Note that the plug-in allows you to store all your messages (or a selection) in a single MBOX file, which in some ways makes it easier to manage. If you want to store folders too, the plug-in will store the contents of every folder as a separate file.

In the latter case, even though my drafts folder is completely empty, the plugin still creates a huge drafts file. Not sure why that is. I am not sure you would want to hold on to the things you ultimately decided not to put in an e-mail, so I would delete that file before writing it to a back-up medium.

Storing other things

Don’t forget that your e-mail client contains other data than e-mail. MozBackup will back up all items (it seems to simply copy the folder on your HD where Thunderbird keeps everything related to your account) but Import/export Tools won’t. The address book in Thunderbird has its own Import/Export menus under Extra.

MozBackup may store your e-mail passwords too, which is presumably why you are given the option to password protect your back-up. I haven’t checked this however.

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