Frequently Asked Questions
Most recent FAQ.
If you don’t get hints here, feel free to ask in our chat room, our mailing list or search in the archives.
- Where do I get offlineimap?
- How fast is it?
- What platforms does offlineimap support?
- Does offlineimap supports XDG Base Directory specification?
- Does offlineimap support mbox, mh, or anything else other than Maildir?
- What is the UID validity problem for folder?
- How do I automatically delete a folder?
- May I delete local folders?
- Can I run multiple instances?
- Can I copy messages between folders?
- Does offlineimap support POP?
- How is offlineimap conformance?
- Can I force offlineimap to sync a folder right now?
- Case sensitivity
- Configuration Questions
- Can I synchronize multiple accounts with offlineimap?
- How do I specify the names of folders?
- How do I prevent certain folders from being synced?
- What is the mailbox name recorder (mbnames) for?
- Does offlineimap verify SSL certificates?
- How do I generate an
- Checking the SSL certificate
- IMAP Server Notes
- Client Notes
- What can I configure? Is there a list of options?
- Advanced questions
- Miscellaneous Questions
Where do I get offlineimap?
See the information at the project homepage.
How fast is it?
Offlineimap has a multithreaded sync, so it should have very nice performance.
maxconnections options are deprecated. Learn why.
A good way to experiment is by setting
maxsyncaccounts = 3 and
= 3 in each account clause. This lets offlineimap open up multiple connections
simultaneously. That will let it process multiple folders and messages at once.
In most cases, this will increase performance of the sync.
Don’t set the number too high. If you do that, things might actually slow down as your link gets saturated. Also, too many connections can cause mail servers to have excessive load. Administrators might take unkindly to this, and the server might bog down. There are many variables in the optimal setting; experimentation may help.
Synchronization Performance section in the
offlineimap(1) man page
for some tips.
What platforms does offlineimap support?
It should run on most platforms supported by Python, with one exception: we do not support Windows, but some have made it work there.
The following has been reported by offlineimap users. We do not test offlineimap on Windows, so we can’t directly address their accuracy.
The basic answer is that it’s possible and doesn’t require hacking offlineimap source code. However, it’s not necessarily trivial. The information below is based in instructions submitted by Chris Walker:
First, you must run offlineimap in the Cygwin environment. The Windows filesystem is not powerful enough to accomodate Maildir by itself.
Next, you’ll need to mount your Maildir directory in a special way. There is information for doing that at barnson.org. That site gives this example:
mount -f -s -b -o managed "d:/tmp/mail" "/home/of/mail"
That URL also has more details on making offlineimap work with Windows.
Does offlineimap supports XDG Base Directory specification?
Yes. We are trying to use
$XDG_CONFIG_HOME/offlineimap/config as the primary
configuration file, falling back to
~/.offlineimaprc if configuration file
location was not explicitely specified at the command line.
Does offlineimap support mbox, mh, or anything else other than Maildir?
Not directly. Maildir was the easiest to implement. We are not planning to write an mbox-backend, though if someone sends well-written mbox support and pledged to support it, it would be committed it to the tree.
However, offlineimap can directly sync accounts on two different IMAP servers together. So you could install an IMAP server on your local machine that supports mbox, sync to it, and then instruct your mail readers to use the mboxes.
Or you could install whatever IMAP server you like on the local machine, and point your mail readers to that IMAP server on localhost.
What is the UID validity problem for folder?
IMAP servers use a folder UIDVALIDITY value in combination with a unique ID (UID) to refer to a specific message. This is guaranteed to be unique to a particular message forever. No other message in the same folder will ever get the same UID as long as UIDVALIDITY remains unchanged. UIDs are an integral part of offlineimap’s synchronization scheme; they are used to match up messages on your computer to messages on the server.
Sometimes, the UIDs on the server might get reset. Usually this will happen if you delete and then recreate a folder. When you create a folder, the server will often start the UID back from 1. But offlineimap might still have the UIDs from the previous folder by the same name stored. Offlineimap will detect this condition because of the changed UIDVALIDITY value and skip the folder. This is GOOD, because it prevents data loss.
In the IMAP/Maildir case, you can fix it by removing your cache data. For instance, you’d type this:
Of course, replace
RemoteRepositoryName with the names as
The reason is that moving it like this means like “I’ve never synced this
folder before, do a full sync the next time”.
Next time you run offlineimap, it will match UIDs of all Local and Remote mails and will download the ones which are not yet existing in the local repository.
Some IMAP servers are broken and do not support UIDs properly. If you continue to get this error for all your folders even after performing the above procedure, it is likely that your IMAP server falls into this category.
Offlineimap is incompatible with such servers. It will not destroy any mail, but at the same time, it won’t actually synchronize it either. Offlineimap will detect this condition and abort prior to synchronization.
This question comes up frequently. See the mailing list archive. You can find a detailed discussion of the problem.
How do I automatically delete a folder?
Offlineimap does not currently provide this feature. You will have to delete folders manually. See next entry too.
May I delete local folders?
Prior to v7.0.0
Offlineimap does a two-way synchronization. That is, if you make a change to the mail on the server, it will be propagated to your local copy, and vise-versa.
Some people might think that it would be wise to just delete all their local mail folders periodically. Offlineimap will take this as an intentional deletion of many messages and will interpret your action as requesting them to be deleted from the server as well.
Starting with v7.0.0, offlineimap won’t delete emails if the directory is removed when the parent directory still exists. Instead, it will re-download the folder. In order to remove all the emails of a folder, it is necessary to remove all the files inside the maildir.
See the “deletions” entry in the “KNOWN ISSUES” section of the man page.
To prevent from any deletion, it’s possible to set the
sync_deletes = no
configuration option. See details in
Can I run multiple instances?
Yes. Offlineimap prevents any attempt to sync the same account over different instances.
Actually, this is the prefered way for syncing more than one account concurrently. Learn more in this blog post.
Can I copy messages between folders?
Normally, when you copy a message between folders or add a new message to a folder locally, offlineimap will just do the right thing. However, sometimes this can be tricky ― if your IMAP server does not provide the SEARCH command, or does not return something useful, offlineimap cannot determine the new UID of the message. So, in these rare instances, offlineimap will upload the message to the IMAP server and delete it from your local folder. Then, on your next sync, the message will be re-downloaded with the proper UID. Offlineimap makes sure that the message was properly uploaded before deleting it, so there should be no risk of data loss.
But if you try to sync between two IMAP servers, where both are unable to provide you with UID of the new message, then this will lead to infinite loop. Offlineimap will upload the message to one server and delete on second. On next run it will upload the message to second server and delete on first, etc.
Does offlineimap support POP?
How is offlineimap conformance?
- Internet Message Access Protocol version 4rev1 (IMAP 4rev1) as specified in RFC 3501.
- CRAM-MD5 as specified in RFC 2195.
- Maildir as specified in the Maildir manpage and the qmail website.
- Standard Python 2.7+ as implemented on POSIX-compliant systems.
Can I force offlineimap to sync a folder right now?
1) if you use the
Blinkenlights UI. That UI shows the active accounts as
4: [active] *Control: . 3: [ 4:36] personal: 2: [ 3:37] work: . 1: [ 6:28] uni:
Simply press the appropriate digit (
personal, etc.) to resync that
account immediately. This will be ignored if a resync is already in progress
for that account.
2) While in sleep mode, you can also send a
SIGUSR1. See the
section in the
offlineimap(1) man page for details.
Offlineimap stuck while downloading
You should make sure the local file system used by Offlineimap is case sensitive. Otherwise, offlineimap might go into troubles. IMAP servers are usually case sensitive.
If you don’t have the choice, it’s possible to manually check there’s no conflicts in the folder names.
I get a “Mailbox already exists” error
Q: When synchronizing, I receive errors such as:
Folder 'sent'[main-remote] could not be created. Server responded: ('NO', ['Mailbox already exists.'])
A: IMAP folders are usually case sensitive. But some IMAP servers seem to
treat “special” folders as case insensitive (e.g. the initial
INBOX. part, or
folders such as
Trash). If you happen to have a folder
sent on one
side of things and a folder called
Sent on the other side, offlineimap will
try to create those folders on both sides. If you server happens to treat those
folders as case-insensitive you can then see this warning.
You can solve this by excluding the
sent folder by filtering it from the
’%’ must be followed by ‘%’ or ‘(‘, found: ‘%!f’
You likely want to use %% to encode the percentage sign, even if it’s stored in the password.
Can I synchronize multiple accounts with offlineimap?
Just name them all in the accounts line in the general section of the configuration file, and add a per-account section for each one.
You can also optionally use the
-a option when you run offlineimap to request
that it only operate upon a subset of the accounts for a particular run.
How do I specify the names of folders?
You do not need to. Offlineimap is smart enough to automatically figure out what folders are present on the IMAP server and synchronize them. You can use the folderfilter and nametrans configuration file options to request only certain folders and rename them as they come in if you like.
Also you can configure offlineImap to only synchronize “subscribed” folders.
How do I prevent certain folders from being synced?
Use the folderfilter option. See
offlineimap.conf for details.
What is the mailbox name recorder (mbnames) for?
Some mail readers, such as mutt, are not capable of automatically determining
the names of your mailboxes. Offlineimap can help these programs by writing the
names of the folders in a format you specify. See
Does offlineimap verify SSL certificates?
You can verify an imapserver’s certificate by specifying the CA certificate on a
per-repository basis by setting the
sslcacertfile option in the config file.
(See the example
offlineimap.conf for details.) If you do not specify any CA
certificate, you will be presented with the server’s certificate fingerprint and
add that to the configuration file, to make sure it remains unchanged. No
verification happens if connecting via STARTTLS.
How do I generate an
sslcacertfile file must contain an SSL certificate (or a concatenated
certificates chain) in PEM format. (See the documentation of
certfile parameter for the gory details.) You can use either openssl or
gnutls to create a certificate file in the required format.
/etc/ssl/certs is not standardized; your system may store SSL
certificates elsewhere. (On some systems it may be in
Checking the SSL certificate
Before using the resulting file, ensure that openssl verified the certificate successfully. In case of problems, you can test the certificate using a command such as (credits to Daniel Shahaf for this) to verify the certificate:
Make sure to empty the
SSL_CERT_DIR environment variable.
If the server uses STARTTLS, pass the
-starttls option and the ‘imap’ port.
View the fingerprint
IMAP Server Notes
In general, offlineimap works with any IMAP server that provides compatibility with the IMAP RFCs. Some servers provide imperfect compatibility that may be good enough for general clients. Offlineimap needs more features, specifically support for UIDs, in order to do its job accurately and completely.
Exchange and Office365
Microsoft products tend to not be full IMAP compliant and add limitations on top of IMAP.
It is required to folderfilter the Calendar mailbox. As reported, some other folders might need to be filtered:
folderfilter = lambda folder: folder not in [ 'Calendar', 'Calendar/Birthdays', 'Calendar/Sub Folder 1', 'Calendar/Sub Folder 2', 'Calendar/United States holidays', 'Contacts', 'Contacts/Sub Folder 1', 'Contacts/Sub Folder 2', 'Contacts/Skype for Business Contacts', 'Deleted Items', 'Drafts', 'Journal', 'Junk Email', 'Notes', 'Outbox', 'Sync Issues', 'Sync Issues/Conflicts', 'Sync Issues/Local Failures', 'Sync Issues/Server Failures', 'Tasks', 'Tasks/Sub Folder 1', 'Tasks/Sub Folder 2' ]
We’ve had reports (here and here) that Davmail must be configured with the keepalive option disabled. Otherwise, some folders might not be synced properly.
What clients does offlineimap work with?
Any client that supports Maildir. Popular ones include mutt, Evolution and KMail. Thunderbird does not have maildir suppport.
With offlineimap’s IMAP-to-IMAP syncing, this can be even wider; see the next question.
Offlineimap can work with Evolution. To do so, first configure your offlineimap
account to have
sep = / in its configuration. Then, configure Evolution with
the “Maildir-format mail directories” server type. For the path, you will need
to specify the name of the top-level folder inside your offlineimap storage
location. You’re now set!
At this time, I believe that offlineimap with Maildirs is not compatible with KMail. KMail cannot work in any mode other than to move all messages out of all folders immediately, which (besides being annoying and fundamentally broken) is incompatible with offlineimap.
However, I have made KMail version 3 work well with offlineimap by installing an IMAP server on my local machine, having offlineimap sync to that, and pointing KMail at the same server.
Another way to see mails downloaded with offlineimap in KMail (KDE4) is to
create a local folder (e.g. Backup) and then use
Maybe you have to rebuild the index of the new folder. Works well with KMail
1.11.4 (KDE4.x), offlineimap 6.1.2 and ArchLinux and
sep = / in
Do I need to use “set maildir_trash”?
Other IMAP sync programs require you to do this. Offlineimap does not. You’ll get the best results without it, in fact, though turning it on won’t hurt anything.
How do I set up mbnames with mutt?
The example offlineimap.conf file has this example. In your
you’ll list this:
Then in your
You might also want to set:
What can I configure? Is there a list of options?
Yes, there is! Have a look here.
How to migrate of IMAP server?
The procedure is quite the same as making a backup and restore it.
I’m using git to install offlineimap and found these branches called “master”, “maint”, “next” and “pu”. What are they?
To be brief:
- master: classical mainline branch.
- next: this is the branch for recent merged patches. Used for testing offlineimap.
- pu (“proposed updates”): patches not ready for inclusion. This should never be checkouted!
- maint: our long-living maintenance branch. We maintain this branch (security and bugfixes) for users who don’t want or can’t upgrade to the latest release.
For more information about the branching model and workflow, see Git Advanced.
Why are your Maildir message filenames so long?
Offlineimap has two relevant principles:
- Never modifying your messages in any way.
- Ensure 100% reliable synchronizations.
In order to do a reliable sync, offlineimap must have a way to uniquely identify each e-mail. Three pieces of information are required to do this: your account name, the folder name, and the message UID. The account name can be calculated from the path in which your messages are. The folder name can usually be as well, BUT some mail clients move messages between folders by simply moving the file, leaving the name intact.
So, offlineimap must store both a message UID and a folder ID. The folder ID is necessary so offlineimap can detect a message being moved to a different folder. Offlineimap stores the UID (U= number) and an md5sum of the foldername (FMD5= number) to facilitate this.
What can I do to ensure offlineimap is still running and hasn’t crashed?
This shell script will restart offlineimap if it has crashed. Sorry, its written in Korn, so you’ll need ksh, pdksh, or mksh to run it:
How to test offlineimap?
We don’t have well testing tool, for now. As an IMAP client, we need an available IMAP server for that purpose. But it doesn’t mean you can do anything.
Recent patches are merged in the
next branch before being in the mainline.
Once you have your own copy of the official repository, track this
Update this branch in a regular basis with:
Notice you’re not supposed to install offlineimap each time. You may simply run it like this:
The choice is up to you. :-)
How to submit a patch?
Read the documentation for contributors.