OfflineIMAP Manual

Powerful IMAP/Maildir synchronization and reader support

Author:John Goerzen <> & contributors


OfflineImap operates on a REMOTE and a LOCAL repository and synchronizes emails between them, so that you can read the same mailbox from multiple computers. The REMOTE repository is some IMAP server, while LOCAL can be either a local Maildir or another IMAP server.

Missing folders will be automatically created on both sides if needed. No folders will be deleted at the moment.

Configuring OfflineImap in basic mode is quite easy, however it provides an amazing amount of flexibility for those with special needs. You can specify the number of connections to your IMAP server, use arbitrary python functions (including regular expressions) to limit the number of folders being synchronized. You can transpose folder names between repositories using any python function, to mangle and modify folder names on the LOCAL repository. There are six different ways to hand the IMAP password to OfflineImap from console input, specifying in the configuration file, .netrc support, specifying in a separate file, to using arbitrary python functions that somehow return the password. Finally, you can use IMAPs IDLE infrastructure to always keep a connection to your IMAP server open and immediately be notified (and synchronized) when a new mail arrives (aka Push mail).

Most configuration is done via the configuration file. However, any setting can also be overriden by command line options handed to OfflineIMAP.

OfflineImap is well suited to be frequently invoked by cron jobs, or can run in daemon mode to periodically check your email (however, it will exit in some error situations).

The documentation is included in the git repository and can be created by issueing make dev-doc in the doc folder (python-sphinx required), or it can be viewed online at


OfflineIMAP is regulated by a configuration file that is normally stored in ~/.offlineimaprc. OfflineIMAP ships with a file named offlineimap.conf that you should copy to that location and then edit. This file is vital to proper operation of the system; it sets everything you need to run OfflineIMAP. Full documentation for the configuration file is included within the sample file.

OfflineIMAP also ships a file named offlineimap.conf.minimal that you can also try. It’s useful if you want to get started with the most basic feature set, and you can read about other features later with offlineimap.conf.

Check out the Use Cases section for some example configurations.


The command line options are described by issueing offlineimap –help. Details on their use can be found either in the sample offlineimap.conf file or in the user docs at

User Interfaces

OfflineIMAP has various user interfaces that let you choose how the program communicates information to you. The ‘ui’ option in the configuration file specifies the user interface. The -u command-line option overrides the configuration file setting. The available values for the configuration file or command-line are described in this section.


Blinkenlights is an interface designed to be sleek, fun to watch, and informative of the overall picture of what OfflineIMAP is doing.

Blinkenlights contains a row of “LEDs” with command buttons and a log. The log shows more detail about what is happening and is color-coded to match the color of the lights.

Each light in the Blinkenlights interface represents a thread of execution – that is, a particular task that OfflineIMAP is performing right now. The colors indicate what task the particular thread is performing, and are as follows:

  • Black:

    indicates that this light’s thread has terminated; it will light up again later when new threads start up. So, black indicates no activity.

  • Red (Meaning 1):

    is the color of the main program’s thread, which basically does nothing but monitor the others. It might remind you of HAL 9000 in 2001.

  • Gray:

    indicates that the thread is establishing a new connection to the IMAP server.

  • Purple:

    is the color of an account synchronization thread that is monitoring the progress of the folders in that account (not generating any I/O).

  • Cyan:

    indicates that the thread is syncing a folder.

  • Green:

    means that a folder’s message list is being loaded.

  • Blue:

    is the color of a message synchronization controller thread.

  • Orange:

    indicates that an actual message is being copied. (We use fuchsia for fake messages.)

  • Red (meaning 2):

    indicates that a message is being deleted.

  • Yellow / bright orange:

    indicates that message flags are being added.

  • Pink / bright red:

    indicates that message flags are being removed.

  • Red / Black Flashing:

    corresponds to the countdown timer that runs between synchronizations.

The name of this interfaces derives from a bit of computer history. Eric Raymond’s Jargon File defines blinkenlights, in part, as:

Front-panel diagnostic lights on a computer, esp. a dinosaur. Now that dinosaurs are rare, this term usually refers to status lights on a modem, network hub, or the like.

This term derives from the last word of the famous blackletter-Gothic sign in mangled pseudo-German that once graced about half the computer rooms in the English-speaking world. One version ran in its entirety as follows:


Das computermachine ist nicht fuer gefingerpoken und mittengrabben.
Ist easy schnappen der springenwerk, blowenfusen und poppencorken
mit spitzensparken. Ist nicht fuer gewerken bei das dumpkopfen.
Das rubbernecken sichtseeren keepen das cotten-pickenen hans in das
pockets muss; relaxen und watchen das blinkenlichten.


TTYUI interface is for people running in terminals. It prints out basic status messages and is generally friendly to use on a console or xterm.


Basic is designed for situations in which OfflineIMAP will be run non-attended and the status of its execution will be logged. This user interface is not capable of reading a password from the keyboard; account passwords must be specified using one of the configuration file options. For example, it will not print periodic sleep announcements and tends to be a tad less verbose, in general.


It will output nothing except errors and serious warnings. Like Basic, this user interface is not capable of reading a password from the keyboard; account passwords must be specified using one of the configuration file options.


MachineUI generates output in a machine-parsable format. It is designed for other programs that will interface to OfflineIMAP.

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. Use maxconnections > 1. By default we only use one connection to an IMAP server. Using 2 or even 3 speeds things up considerably in most cases. This setting goes into the [Repository XXX] section.
  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 the example offlineimap.conf.
  3. The default status cache is a plain text file that will write 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 slower. I recommend to use the sqlite backend for that. See the status_backend = sqlite setting in the example offlineimap.conf. You will need to have python-sqlite installed in order to use this. This will save you plenty of disk activity. Do note that the sqlite backend is still considered experimental as it has only been included recently (although a loss of your status cache should not be a tragedy as that file can be rebuild automatically)
  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. Eg, I 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 continueing, you can set this to True. If you set it to False, you lose some of that safety, trading it for speed.

Upgrading from plain text cache to SQLITE based cache

OfflineImap uses a cache to store the last know status of mails (flags etc). Historically that has meant plain text files, but recently we introduced sqlite-based cache, which helps with performance and CPU usage on large folders. Here is how to upgrade existing plain text cache installations to sqlite based one:

  1. Sync to make sure things are reasonably similar
  2. Change the account section to status_backend = sqlite
  3. A new sync will convert your plain text cache to an sqlite cache (but leave the old plain text cache around for easy reverting) This should be quick and not involve any mail up/downloading.
  4. See if it works :-)
  5. If it does not work, go back to the old version or set status_backend=plain
  6. Or, once you are sure it works, you can delete the .offlineimap/Account-foo/LocalStatus folder (the new cache will be in the LocalStatus-sqlite folder)

Security and SSL

Some words on OfflineImap and its use of SSL/TLS. By default, we 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 fingerprint is being planned, it is not implemented yet. 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 contains an entry on how to create your own certificate and CA certificate.


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. Do note, that 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 and SIGUSR2.

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, 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”.

Folder filtering and nametrans

OfflineImap offers flexible (and complex) ways of filtering and transforming folder names. Please see the docs/dev-docs-src/folderfilters.rst document about details how to use folder filters and name transformations. The documentation will be autogenerated by a “make dev-doc” in the docs directory. It is also viewable at Folder filtering and Name translation.


  • SSL3 write pending:

    users enabling SSL may hit a bug about “SSL3 write pending”. If so, the account(s) will stay unsynchronised from the time the bug appeared. Running OfflineIMAP again can help. We are still working on this bug. Patches or detailed bug reports would be appreciated. Please check you’re running the last stable version and send us a report to the mailing list including the full log.

  • IDLE support is incomplete and experimental. Bugs may be encountered.

    • No hook exists for “run after an IDLE response”. Email will show up, but may not be processed until the next refresh cycle.
    • nametrans may not be supported correctly.
    • IMAP IDLE <-> IMAP IDLE doesn’t work yet.
    • IDLE may only work “once” per refresh. If you encounter this bug, please send a report to the list!
  • Maildir support in Windows drive

    Maildir uses colon caracter (:) in message file names. Colon is however forbidden character in windows drives. There are several workarounds for that situation:

    • Use “maildir-windows-compatible = yes” account OfflineIMAP configuration.
      • That makes OfflineIMAP to use exclamation mark (!) instead of colon for storing messages. Such files can be written to windows partitions. But you will probably loose compatibility with other programs trying to read the same Maildir.
      • Exclamation mark was chosen because of the note in
      • If you have some messages already stored without this option, you will have to re-sync them again
    • Enable file name character translation in windows registry (not tested)
    • Use cygwin managed mount (not tested)
      • not available anymore since cygwin 1.7


Sharing a maildir with multiple IMAP servers

Generally a word of caution mixing IMAP repositories on the same Maildir root. You have to be careful that you never use the same maildir folder for 2 IMAP servers. In the best case, the folder MD5 will be different, and you will get a loop where it will upload your mails to both servers in turn (infinitely!) as it thinks you have placed new mails in the local Maildir. In the worst case, the MD5 is the same (likely) and mail UIDs overlap (likely too!) and it will fail to sync some mails as it thinks they are already existent.

I would create a new local Maildir Repository for the Personal Gmail and use a different root to be on the safe side here. You could e.g. use ~/mail/Pro as Maildir root for the ProGmail and ~/mail/Personal as root for the personal one.

If you then point your local mutt, or whatever MUA you use to ~/mail/ as root, it should still recognize all folders. (see the 2 IMAP setup in the Use Cases section.


Sync from GMail to another IMAP server

This is an example of a setup where “TheOtherImap” requires all folders to be under INBOX:

[Repository Gmailserver-foo]
#This is the remote repository
type = Gmail
remotepass = XXX
remoteuser = XXX
# The below will put all GMAIL folders as sub-folders of the 'local' INBOX,
# assuming that your path separator on 'local' is a dot.
nametrans = lambda x: 'INBOX.' + x

[Repository TheOtherImap]
#This is the 'local' repository
type = IMAP
remotehost = XXX
remotepass = XXX
remoteuser = XXX
#Do not use nametrans here.

Selecting only a few folders to sync

Add this to the remote gmail repository section to only sync mails which are in a certain folder:

folderfilter = lambda folder: folder.startswith('MyLabel')

To only get the All Mail folder from a Gmail account, you would e.g. do:

folderfilter = lambda folder: folder.startswith('[Gmail]/All Mail')

Another nametrans transpose example

Put everything in a GMX. subfolder except for the boxes INBOX, Draft, and Sent which should keep the same name:

nametrans: lambda folder: folder if folder in ['INBOX', 'Drafts', 'Sent'] \
                          else re.sub(r'^', r'GMX.', folder)

2 IMAP using name translations

Synchronizing 2 IMAP accounts to local Maildirs that are “next to each other”, so that mutt can work on both. Full email setup described by Thomas Kahle at


accounts = acc1, acc2
maxsyncaccounts = 2
ui = ttyui
socktimeout = 90

[Account acc1]
localrepository = acc1local
remoterepository = acc1remote
autorefresh = 2

[Account acc2]
localrepository = acc2local
remoterepository = acc2remote
autorefresh = 4

[Repository acc1local]
type = Maildir
localfolders = ~/Mail/acc1

[Repository acc2local]
type = Maildir
localfolders = ~/Mail/acc2

[Repository acc1remote]
type = IMAP
remotehost =
remoteusereval = get_username("")
remotepasseval = get_password("")
nametrans = oimaptransfolder_acc1
ssl = yes
maxconnections = 2
# Folders to get:
folderfilter = lambda foldername: foldername in [
             'INBOX', 'Drafts', 'Sent', 'archiv']

[Repository acc2remote]
type = IMAP
remotehost =
remoteusereval = get_username("")
remotepasseval = get_password("")
nametrans = oimaptransfolder_acc2
ssl = yes
maxconnections = 2

One of the coolest things about offlineimap is that you can call arbitrary python code from your configuration. To do this, specify a pythonfile with:


Your pythonfile needs to contain implementations for the functions that you want to use in offflineimaprc. The example uses it for two purposes: Fetching passwords from the gnome-keyring and translating folder names on the server to local foldernames. An example implementation of get_username and get_password showing how to query gnome-keyring is contained in The folderfilter is a lambda term that, well, filters which folders to get. The function oimaptransfolder_acc2 translates remote folders into local folders with a very simple logic. The INBOX folder will have the same name as the account while any other folder will have the account name and a dot as a prefix. This is useful for hierarchichal display in mutt. Offlineimap handles the renaming correctly in both directions:

import re
def oimaptransfolder_acc1(foldername):
    if(foldername == "INBOX"):
        retval = "acc1"
        retval = "acc1." + foldername
    retval = re.sub("/", ".", retval)
    return retval

def oimaptransfolder_acc2(foldername):
    if(foldername == "INBOX"):
        retval = "acc2"
        retval = "acc2." + foldername
    retval = re.sub("/", ".", retval)
    return retval
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