maildir with IMAP

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Joined: January 20th, 2017, 1:03 pm

Post Posted January 20th, 2017, 1:13 pm

My setup:
Thunderbird 45.6.0 on a MacBook running MacOS 10.12.2. I have five e-mail accounts, all accessed by IMAP. I frequently go offline and use some local folders. Backups are via Time Machine. My whole profile is about 28GB.

I'm moving to a new MacBook and am doing a fresh install of Thunderbird with a new profile. My plan is to download everything via IMAP and copy over the local folders.

I would like to switch to Maildir storage format, so that Time Machine has an easier time backing up.

My question is whether Maildir is stable and if there are any gotchas with IMAP or local folders.


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Joined: July 30th, 2003, 5:06 pm

Post Posted January 20th, 2017, 8:53 pm

No, its not stable yet. A lot of the problems seem to be when moving/copying messages between accounts. My impression was that many of those gotchas were fixed, but that it still had some aggravating bugs such as "Move to maildir local folders sometimes fail".

See - (maildirblockers) finish "maildir" message storage [meta] and

If your goal is to have the messages in a easy format for the Time Machine to backup I suggest you consider disabling offline folders and global search/indexing, and use a standalone utility that can do incremental backups from a IMAP server to maildir files instead. See for some starting points.

Take a look at offlineimap at and That might work well if you install Python 2.7+ under OSX. However, keep in mind that with a incremental backup you won't lose a message if you delete the original, but you will if you use a tool to "sync" the remote folder and the backup.

Posts: 2
Joined: January 20th, 2017, 1:03 pm

Post Posted January 23rd, 2017, 9:58 pm

Thanks. I go offline too often, so it looks like I'm stuck with mbox.

Steve H
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Joined: August 31st, 2017, 1:06 pm

Post Posted August 31st, 2017, 1:32 pm

I've got a very similar use case. I switched to maildir in April to allow for much more efficient backups - why backup an entire mbox file just because 1 new message arrived?
So while I'm aware of the current issue with copying messages with attachments from an IMAP server when using maildir storage, I have found the following to work: I use a number of rules to manage the organization of messages, including copying/moving msgs into folders under my Local Folders (in maildir format). By copying the message to the Local Folders first, I get the attachments properly copied. The subsequent copy (or move) into another IMAP folder will not properly included the attachment but my work around is knowing it's in my Local Folder. Not ideal but it's consistent.

I use the Local Folder hierarchy for those msgs worth long-term archiving & sharing across platforms. Others I just leave in the IMAP folders since I can use TB or browsers to access those folder as needed.
for bulk archiving (at year end), I do the copies, moves manually. Let nextCloud grind away for a bit and it's working.

By using maildir storage in my Local Folders, I can use nextCloud to sync these files to a drive I can also access from my Windows 7 TB client, Ubuntu TB client, as well as from a Raspbian SBC. Most of my TB msg files are write once, read rarely so the sync ops are pretty darn efficient. Not the case if I had even tried to use mbox storage as some of my more active TB folders are rather large (>>100MB for just the current year, past year's are archives that aren't updated, just cleaned/purged rarely).
I don't sync the msf (index) TB files since they can be rebuilt rather quickly & are best private to each client installation. I've not risked sharing the msf files as I can image issues from having 2 or more TB clients all trying to manage the same index.

so, by using maildir, I avoid having huge numbers of backups of the same 99.9% mbox content. I don't have redundant versions since I'm not modifying received email messages, just reading/searching/archiving. So incremental syncing & backups are now quite practical. And the few IMAP + maildir issues have yet to be show stoppers for me. Hope you're able to find maildir as useful as I've so far.

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