Converting from mbox to maildir

Phil Davis phil.davis at
Thu Jun 18 10:08:06 UTC 2015

As there is no built-in auto-conversion from mbox to maildir format, I 
found that dragging messages or folders from an account in mbox format 
to an account in maildir format achieves the conversion. So it can be 
done in a manual fashion.

I just converted one of my profiles from mbox to maildir by creating a 
new profile with account in maildir format, and using a dummy account in 
mbox format to move folders across, as per the steps below.

I guess it would also be possible to do this in your existing profile - 
switch the default storage for new accounts to maildir, make another 
account (that really just logs in to your existing account - a 
duplicate), drag the folders/mail from old to new account within the 
existing profile, delete the original folders/account. That way all your 
other settings, filters, address books... stay. But it leaves "Local 
Folders" still in mbox format - I didn't quickly think of a way to move 
stuff out of Local Folders, then delete Local Folders and recreate it 
again in maildir format in an existing profile.

Anyway, here are my steps. You do have to think while doing this - so it 
is not quite suitable for an enterprise mass conversion :)

It would be even nicer if you could change the Message Store Type for 
existing accounts and "Local Folders" and have Thunderbird internally 
convert existing message stores.

*Converting from mbox to maildir in Thunderbird 38.0.1*
1) Backup your existing profile!!!
2) In your existing profile, delete your Trash, generally have a 
cleanup, minimise the stuff to move!
3) Backup again after the cleanup.

4) Create a new profile with Thunderbird 38.0.1
5) Cancel out of the wizard that creates an account
6) Tools-Options-Advanced-General - Message Store Type for new accounts: 
change to maildir
7) Tools-Account Settings - Account Actions - Add Mail Account - setup 
your account like you normally would.
Now you have a working email account that can send/receive mail and the 
mail account and Local Folders use maildir storage.

8) Tools-Options-Advanced-General - Message Store Type for new accounts: 
change back to mbox
9) Tools-Account Settings - Account Actions - Add Mail Account - Create 
another account (dummy at - whatever you like).
You will need to put in some rubbish values and use the "Manual Config" 
and then "Advanced Config" buttons to force it to save.
This account uses mbox format for storage.

10) Tools-Options-Advanced-General - Message Store Type for new 
accounts: change back to maildir
11) Exit Thunderbird

12) Go to your old profile, Mail sub-folder and the folders under that 
"Local Folders" and the folder for your old email account/s.
13) The mail is in files in the folder tree that have no file extension, 
plus it does not hurt to copy the *.msf also.
So copy everything from these 2 old sub-folders of "Mail" into the new 
profile, under the "Mail" sub-folder for the 2nd "dummy" account.
You don't need to copy Trash.* - but you can if you want.
Copy Inbox.* and let it overwrite the empty Inbox.* that is in the 2nd 
"dummy" account.
Everything else should just cleanly add itself under the 2nd "dummy" 
account folder of the new profile.

14) Start Thunderbird with the new profile.
You can see all your old mail in folders in the 2nd "dummy" account.
15) Drag folders (folder trees if there is a hierarchy) across to the 
new email account, or to Local Folders.
They convert to maildir format as the folders and messages are copied.
16) In Inbox and Sent of the 2nd "dummy" account (your original Inbox 
and Sent), select all the messages and drag them to the new Inbox/Sent 
of the real new account.

17) When you are happy, delete the old folders from the "dummy" account, 
and then delete the "dummy" account from the profile.
You can clean it out of the profile completely by deleting its folder 
under the new profile Mail folder.

Keep your old profile for some time, until you are happy that you didn't 
forget anything.

Note: The above process just brings across your existing mail.
If you want your address books you will need to export/import those, and 
any other settings like mail filters or...

Phil Davis

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