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From Maildir or mbox

E-mail messages and folders can be easily imported into a user account from either Maildir or mbox mailboxes. The CLI command used to import mailboxes into Stalwart JMAP is import messages and accepts the following options:

Import messages and folders

Usage: stalwart-cli import messages [OPTIONS] --format <FORMAT> <ACCOUNT> <PATH>

Account name or email to import messages into

Path to the mailbox to import, or '-' for stdin (stdin only supported for mbox)

-f, --format <FORMAT>
Possible values:
- mbox: Mbox format
- maildir: Maildir and Maildir++ formats
- maildir-nested: Maildir with hierarchical folders (i.e. Dovecot)

-n, --num-concurrent <NUM_CONCURRENT>
Number of messages to import concurrently, defaults to the number of CPUs

-h, --help
Print help (see a summary with '-h')


The format of the mailbox to be imported is specified with the -f option. The following formats are supported:

  • mbox: Mbox file format. Messages are imported into the account's Inbox folder.
  • maildir: Maildir and Maildir++ mailboxes. Subfolders reside under the main Maildir directory and use . as folder separator.
  • maildir-nested: Maildir mailbox with a file system layout, used mostly by Dovecot.

Concurrent tasks

In order to accelerate the import process, messages are imported in parallel using multiple threads. The default number of threads employed during import equals to the number of CPUs in the system running the CLI tool. To specify a different number of import threads to spawn, use the -n option.


To import a mailbox, specify the account name, path to the mailbox (or - to read the mailbox from standard input) and the mailbox format:

For example, to import a Maildir mailbox into the account john:

$ stalwart-cli -u import messages -f maildir john /home/john/Maildir

The CLI tool will proceed to create any missing mailboxes and spawn multiple message import threads:

[1/4] Parsing mailbox...
[2/4] Fetching existing mailboxes for account...
[3/4] Creating missing mailboxes...
[4/4] Importing messages...
[1/?] ⠂ Importing 72: Inbox/[email protected]
[2/?] ⠂ Importing 65: Inbox/[email protected]
[3/?] ⠂ Importing 66: Inbox/[email protected]
[4/?] ⠂ Importing 67: Inbox/[email protected]
[5/?] ⠂ Importing 68: Inbox/[email protected]
[6/?] ⠁ Importing 61: Sent Items/[email protected]
[7/?] ⠁ Importing 62: Drafts/[email protected]
[8/?] ⠁ Importing 63: Drafts/[email protected]

If the import process is interrupted, the CLI tool supports automatically resuming the task without duplicating messages or folders.


When importing Maildir mailboxes with hundreds of subfolders, some systems may report a Too many open files error:

[1/4] Parsing mailbox...
Failed to read Maildir folder: Too many open files (os error 24)

To increate the maximum number of open files use the ulimit command, for example:

$ ulimit -n 65535