offlineIMAP/docs/offlineimap.txt

offlineimap(1)
==============

NAME
----
offlineimap - Synchronize mailboxes and Maildirs

SYNOPSIS
--------
[verse]
'offlineimap' (options)

DESCRIPTION
-----------

Synchronize the accounts configured in the configuration file via IMAP. Each
account has two sides.  One of the side must be an IMAP server.  The other side
can either be a Maildir or another IMAP server.

Python 3 is supported while still EXPERIMENTAL.


OPTIONS
-------

-h::
--help::

  Display summary of options.

--version::

  Output version.

-V::

  Output offlineimap version and additional imaplib2 information.

--dry-run::

  Run in dry run mode.
+
Do not actually modify any store but check and print what synchronization
actions would be taken if a sync would be performed. It will not precisely
give the exact information what will happen. If e.g. we need to create a
folder, it merely outputs 'Would create folder X', but not how many and which
mails it would transfer.


--info::

  Output information on the configured email repositories.
+
Useful for debugging and bug reporting. Use in conjunction with the `-a' option
to limit the output to a single account. This mode will prevent any actual sync
to occur and exits after it output the debug information.


-1::

  Limit multithreading operations and run solely a single-thread sync.
+
This effectively sets the 'maxsyncaccounts' and all 'maxconnections' configuration
file variables to '1' (the number).


-P <directory>::

  Set OfflineIMAP into profile mode.
+
The program will create DIR (it must not already exist).  As it runs, Python
profiling information about each thread is logged into profiledir. Please
note: This option is present for debugging and optimization only, and should
NOT be used unless you have a specific reason to do so. It will significantly
decrease program performance, may reduce reliability, and can generate huge
amounts of data. This option implies the `-1' option.


-a <account1[,account2[,...]]>::

  Overrides the accounts section in the config file.
+
Allows one to specify a particular account or set of accounts to sync without
having to edit the config file.


-c <path/to/configuration_file>::

  Specifies a configuration file to use.


-d <type1[,type2[,...]]>::

  Enables debugging for OfflineIMAP.
+
This is useful if you are to track down a malfunction or figure out what is
going on under the hood. This option requires one or more debugtypes,
separated by commas. These define what exactly will be debugged, and so far
include options: "imap", "thread", "maildir" or "ALL". The imap option will enable
IMAP protocol stream and parsing debugging. Note that the output may contain
passwords, so take care to remove that from the debugging output before
sending it to anyone else. The maildir option will enable debugging for
certain Maildir operations.  The use of any debug option (unless "thread" is
included), implies the single-thread option `-1'.


-l <path/to/file.log>::

   Send logs to <file.log>.

-s::

   Send logs to syslog.


-f <folder1[,folder1[,...]]>::

    Only sync the specified folders.
+
The folder names are the untranslated foldernames of the remote repository.
This command-line option overrides any 'folderfilter' and 'folderincludes'
options in the configuration file.

-k <[section:]option=value::

  Override any configuration file option.
+
If "section" is omitted, it defaults to "general". Any underscores in the
section name are replaced with spaces: for instance, to override option
"autorefresh" in the "[Account Personal]" section in the config file one would
use `-k Account_Personal:autorefresh=30'. Repeat this option as much as
necessary to redefine multiple options.

-o::

  Run only once.
+
Ignore any autorefresh setting in the configuration file.

-q::

  Run only quick synchronizations.
+
Ignore any flag updates on IMAP servers. If a flag on the remote IMAP changes,
and we have the message locally, it will be left untouched in a quick run. This
option is ignored if maxage is set.


-u <UI>::

  Specifies an alternative user interface to use.
+
This overrides the default specified in the configuration file. The UI
specified with `-u' will be forced to be used, even if checks determine that it
is not usable. Possible interface choices are: quiet, basic, syslog, ttyui,
blinkenlights, machineui.


--delete-folder::
  Delete a folder on the remote repository.
+
Only one account must be specified/configured for this feature to work. The
folder name must be provided in IMAP encoding with the remote separators (likely
'/'). E.g.: "Remote/folder/name".


--migrate-fmd5-using-nametrans::
  Migrate FMD5 hashes from versions prior to 6.3.5.
+
The way that FMD5 hashes are calculated was changed in version 6.3.5 (now using
the nametrans folder name) introducing a regression which may lead to
re-uploading all messages. Try and fix the above regression by calculating the
correct FMD5 values and renaming the corresponding messages.

CAUTION: Since the FMD5 part of the filename changes, this may lead to UID
conflicts. Ensure to dispose a proper backup of both the cache and the Maildir
before running this fix as well as verify the results using the `--dry-run'
flag first.


--mbnames-prune::
  Remove dangling entries for removed accounts or if mbnames is not enabled/used
  anymore.
+
Internally, offlineimap build intermediate mbnames files. They are added
automatically when mbnames is enabled. However, disabling accounts so they are
not synced anymore does not necessarily means they should be removed from the file
built by mbnames. It is required to start offlineimap with this CLI option each
time accounts are removed. When run, any account not in the 'accounts'
configuration option are removed in the mbnames file.
+
It is possible to manually remove intermediate files in '<metadata>/mbnames/'.
+
Notice this option honors --dry-run.


Synchronization Performance
---------------------------

By default, we use fairly conservative settings that are safe for syncing but
that might not be the best performing one. Once you got everything set up and
running, you might want to look into speeding up your synchronization. Here
are a couple of hints and tips on how to achieve this.

1. Synchronize more than one account.
+
By default we only use one connection to an IMAP server. Using 2 or even 3
speeds things up considerably in most cases.  In order to synchronize more than
one account concurrently, consider starting one instance of offlineimap per
account.
+
WARNING: enabling the 'maxsyncaccounts' and 'maxconnections' options is
deprecated since it's known to have race conditions.

2. Use folderfilters.
+
The quickest sync is a sync that can ignore some folders. I sort my inbox into
monthly folders, and ignore every folder that is more than 2-3 months old,
this lets me only inspect a fraction of my Mails on every sync. If you haven't
done this yet, do it :). See the 'folderfilter' section in 'offlineimap.conf'.

3. The sqlite cache.
+
OfflineImap caches the state of the synchronisation to e.g. be able to determine
if a mail has been added or deleted on either side.
+
The historical status cache is a plain text file that writes out the complete
file for each single new message (or even changed flag) to a temporary file. If
you have plenty of files in a folder, this is a few hundred kilo to megabytes
for each mail and is bound to make things slow. The latest default status cache
is sqlite. This saves plenty of disk activity. The sqlite engine and the Python
sqlite module must be installed. Enable the 'status_backend = plain' setting in
'offlineimap.conf' for legacy compatibility with versions prior to '6.4.0'.
+
If you switch the backend from plain to sqlite, you may want to delete the old
cache directory in '<metadata>/Account-<account>/LocalStatus' manually (the
sqlite cache stands in the 'LocalStatus-sqlite' folder).

4. Use quick sync.
+
A regular sync will request all flags and all UIDs of all mails in each folder
which takes quite some time. A quick sync only compares the number of
messages in a folder on the IMAP side (it will detect flag changes on the
Maildir side of things though). A quick sync on my smallish account will take
7 seconds rather than 40 seconds. E.g. run a cron script that does a regular
sync once a day, and does quick syncs `-q' only synchronizing the `-f INBOX'
in between.

5. Turn off fsync.
+
In the '[general]' section you can set fsync to 'True' or 'False'. If you want to
play 110% safe and wait for all operations to hit the disk before continuing,
you can set this to True. If you set it to False, you lose some of that
safety, trading it for speed.


Security and SSL
----------------

By default, OfflineIMAP will connect using any method that 'openssl' supports,
that is SSLv2, SSLv3, or TLSv1.

Do note that SSLv2 is notoriously insecure and deprecated.  Unfortunately,
python2 does not offer easy ways to disable SSLv2. It is recommended you test
your setup and make sure that the mail server does not use an SSLv2
connection. Use e.g. "openssl s_client -host mail.server -port 443" to find
out the connection that is used by default.

* Certificate checking
+
Unfortunately, by default we will not verify the certificate of an IMAP
TLS/SSL server we connect to, so connecting by SSL is no guarantee against
man-in-the-middle attacks. While verifying a server certificate checking the
fingerprint is recommended. There is currently only one safe way
to ensure that you connect to the correct server in an encrypted manner: you
can specify a 'sslcacertfile' setting in your repository section of
offlineimap.conf pointing to a file that contains (among others) a CA
Certificate in PEM format which validating your server certificate. In this
case, we will check that:

1. The server SSL certificate is validated by the CA Certificate.

2. The server host name matches the SSL certificate.

3. The server certificate is not past its expiration date.

The FAQ has an entry on how to create your own certificate and CA certificate.

* StartTLS
+
If you have not configured your account to connect via SSL anyway, OfflineImap
will still attempt to set up an SSL connection via the STARTTLS function, in
case the imap server supports it.
+
There is no certificate or fingerprint checking involved at all, when using
STARTTLS (the underlying imaplib library does not support this yet). This
means that you will be protected against passively listening eavesdroppers and
they will not be able to see your password or email contents. However, this
will not protect you from active attacks, such as Man-In-The-Middle attacks
which cause you to connect to the wrong server and pretend to be your mail
server.
+
*DO NOT RELY ON STARTTLS AS A SAFE CONNECTION GUARANTEEING THE AUTHENTICITY OF
YOUR IMAP SERVER!*


Unix Signals
------------

OfflineImap listens to the unix signals SIGUSR1, SIGUSR2, SIGTERM, SIGINT,
SIGHUP, SIGQUIT.

* If sent a SIGUSR1 it will abort any current (or next future) sleep of all
accounts that are configured to 'autorefresh'. In effect, this will trigger a
full sync of all accounts to be performed as soon as possible.

* If sent a SIGUSR2 or SIGABRT, it will stop 'autorefresh' mode for all
accounts. That is, accounts will abort any current sleep and will exit after a
currently running synchronization has finished. This signal can be used to
gracefully exit out of a running offlineimap "daemon".

* SIGTERM, SIGINT, SIGHUP are all treated to gracefully terminate as soon as
possible. This means it will finish syncing the current folder in each
account, close keep alive connections, remove locks on the accounts and exit.
+
It may take up to 10 seconds, if autorefresh option is used.
+
More than one SIGTERM will behave like SIGQUIT.

* If sent SIGQUIT, dumps stack traces for all threads and tries to dump
process core.


Known Issues
------------

include::./offlineimap.known_issues.txt[]


Main authors
------------

  John Goerzen, Sebastian Spaetz, Eygene Ryabinkin, Nicolas Sebrecht.


See Also
--------

  offlineimapui(7), openssl(1), signal(7), sqlite3(1).
  http://www.offlineimap.org