Provided by: isync_1.4.4-5build3_amd64 
NAME
mbsync - synchronize IMAP4 and Maildir mailboxes
SYNOPSIS
mbsync [options ...] {{channel[:box[{,|\n}...]]|group} ...|-a}
DESCRIPTION
mbsync is a command line application which synchronizes mailboxes; currently Maildir and IMAP4 mailboxes
are supported. New messages, message deletions and flag changes can be propagated both ways; the
operation set can be selected in a fine-grained manner.
Synchronization is based on unique message identifiers (UIDs), so no identification conflicts can occur
(unlike with some other mail synchronizers). OTOH, mbsync is susceptible to UID validity changes (but
will recover just fine if the change is unfounded). Synchronization state is kept in one local text file
per mailbox pair; these files are protected against concurrent mbsync processes. Mailboxes can be safely
modified while mbsync operates (see INHERENT PROBLEMS below for a minor exception). Multiple replicas of
each mailbox can be maintained.
OPTIONS
-c, --config file
Read configuration from file. By default, the configuration is read from ~/.mbsyncrc.
-a, --all
Select all configured channels. Any channel/group specifications on the command line are ignored.
-l, --list
Don't synchronize anything, but list all mailboxes in the selected channels and exit.
-C[f][n], --create[-far|-near]
Override any Create options from the config file. See below.
-R[f][n], --remove[-far|-near]
Override any Remove options from the config file. See below.
-X[f][n], --expunge[-far|-near]
Override any Expunge options from the config file. See below.
{-n|-N|-d|-f|-0|-F}, {--new|--renew|--delete|--flags|--noop|--full}
{-L|-H}[n][N][d][f], {--pull|--push}[-new|-renew|-delete|-flags]
Override any Sync options from the config file. See below.
-h, --help
Display a summary of command line options.
-v, --version
Display version information.
-V, --verbose
Enable verbose mode, which displays what is currently happening.
-D[C][d|D][m][M][n|N][s]], --debug[-crash|-driver|-driver-all|-maildir|-main|-net|-net-all|-sync]
Enable debugging categories:
C, crash - use built-in crash handler
d, driver - print driver calls (metadata only)
D, driver-all - print driver calls (including messages)
m, maildir - print maildir debug info
M, main - print main debug info
n, net - print network traffic (protocol only)
N, net-all - print network traffic (including payloads)
s, sync - print synchronization debug info
All categories except crash implictly enable verbose mode. Without category specification, all
categories except net-all are enabled.
-q, --quiet
Suppress progress counters (this is implicit if stdout is no TTY, or any debugging categories are
enabled) and notices. If specified twice, suppress warning messages as well.
CONFIGURATION
The configuration file is mandatory; mbsync will not run without it. Lines starting with a hash mark (#)
are comments and are ignored entirely. Configuration items are keywords followed by one or more
arguments; arguments containing spaces must be enclosed in double quotes ("), and literal double quotes
and backslashes (\) must be backslash-escaped. All keywords (including those used as arguments) are
case-insensitive. Bash-like home directory expansion using the tilde (~) is supported in all options
which represent local paths. There are a few global options, the others apply to particular sections.
Sections begin with a section-starting keyword and are terminated by an empty line or end of file. Every
section defines an object with an identifier unique within that object class.
There are two basic object classes: Stores and Channels. A Store defines a collection of mailboxes;
basically a folder, either local or remote. A Channel connects two Stores, describing the way the two
are synchronized.
There are two auxiliary object classes: Accounts and Groups. An Account describes the connection part of
network Stores, so server configurations can be shared between multiple Stores. A Group aggregates
multiple Channels to save typing on the command line.
File system locations (in particular, Path and Inbox) use the Store's internal path separators, which may
be slashes, periods, etc., or even combinations thereof.
Mailbox names, OTOH, always use canonical path separators, which are Unix-like forward slashes.
All Stores
These options can be used in all supported Store types.
In this context, the term "remote" describes the second Store within a Channel, and not necessarily a
remote server.
The special mailbox INBOX exists in every Store; its physical location in the file system is Store type
specific.
Path path
The location of the Store in the (server's) file system. If this is no absolute path, the
reference point is Store type specific. This string is prepended to the mailbox names addressed
in this Store, but is not considered part of them; this is important for Patterns and Create in
the Channels section. Note that you must append a slash if you want to specify an entire
directory. (Default: none)
MaxSize size[k|m][b]
Messages larger than size will have only a small placeholder message propagated into this Store.
To propagate the full message, it must be flagged in either Store; that can be done retroactively,
in which case the ReNew operation needs to be executed instead of New. This is useful for
avoiding downloading messages with large attachments unless they are actually needed. Caveat:
Setting a size limit on a Store you never read directly (which is typically the case for servers)
is not recommended, as you may never notice that affected messages were not propagated to it.
K and M can be appended to the size to specify KiBytes resp. MeBytes instead of bytes. B is
accepted but superfluous. If size is 0, the maximum message size is unlimited. (Default: 0)
MapInbox mailbox
Create a virtual mailbox (relative to Path) which aliases the INBOX. Makes sense in conjunction
with Patterns in the Channels section, though with a Maildir near side, you probably want to place
Inbox under Path instead. This virtual mailbox does not support subfolders.
Flatten delim
Flatten the hierarchy within this Store by substituting the canonical hierarchy delimiter / with
delim. This can be useful when the MUA used to access the Store provides suboptimal handling of
hierarchical mailboxes, as is the case with Mutt. A common choice for the delimiter is ..
Note that flattened sub-folders of the INBOX always end up under Path, including the "INBOXdelim"
prefix.
Trash mailbox
Specifies a mailbox (relative to Path) to copy deleted messages to prior to expunging. See
RECOMMENDATIONS and INHERENT PROBLEMS below. (Default: none)
TrashNewOnly yes|no
When trashing, copy only not yet propagated messages. This makes sense if the remote Store has a
Trash as well (with TrashNewOnly no). (Default: no)
TrashRemoteNew yes|no
When expunging the remote Store, copy not yet propagated messages to this Store's Trash. When
using this, the remote Store does not need an own Trash at all, yet all messages are archived.
(Default: no)
Maildir Stores
The reference point for relative Paths is the current working directory.
As mbsync needs UIDs, but no standardized UID storage scheme exists for Maildir, mbsync supports two
schemes, each with its pros and cons.
The native scheme is stolen from the latest Maildir patches to c-client and is therefore compatible with
pine. The UID validity is stored in a file named .uidvalidity; the UIDs are encoded in the file names of
the messages.
The alternative scheme is based on the UID mapping used by isync versions 0.8 and 0.9.x. The invariant
parts of the file names of the messages are used as keys into a Berkeley database named .isyncuidmap.db,
which holds the UID validity as well.
The native scheme is faster, more space efficient, endianness independent and "human readable", but will
be disrupted if a message is copied from another mailbox without getting a new file name; this would
result in duplicated UIDs sooner or later, which in turn results in a UID validity change, making
synchronization fail. The alternative scheme would fail if a MUA changed a message's file name in a part
mbsync considers invariant; this would be interpreted as a message deletion and a new message, resulting
in unnecessary traffic.
Mutt is known to work fine with both schemes.
Use mdconvert to convert mailboxes from one scheme to the other.
MaildirStore name
Define the Maildir Store name, opening a section for its parameters.
AltMap yes|no
Use the alternative UID storage scheme for mailboxes in this Store. This does not affect
mailboxes that do already have a UID storage scheme; use mdconvert to change it. See
RECOMMENDATIONS below. (Default: no)
Inbox path
The location of the INBOX. This is not relative to Path, but it is allowed to place the INBOX
inside the Path. (Default: ~/Maildir)
InfoDelimiter delim
The character used to delimit the info field from a message's basename. The Maildir standard
defines this to be the colon, but this is incompatible with DOS/Windows file systems. (Default:
the value of FieldDelimiter)
SubFolders Verbatim|Maildir++|Legacy
The on-disk folder naming style used for hierarchical mailboxes. This option has no effect when
Flatten is used.
Suppose mailboxes with the canonical paths top/sub/subsub and INBOX/sub/subsub, the styles will
yield the following on-disk paths:
Verbatim - Path/top/sub/subsub and Inbox/sub/subsub (this is the style you probably want to use)
Maildir++ - Inbox/.top.sub.subsub and Inbox/..sub.subsub (this style is compatible with Courier
and Dovecot - but note that the mailbox metadata format is not compatible). Note that attempts to
set Path are rejected in this mode.
Legacy - Path/top/.sub/.subsub and Inbox/.sub/.subsub (this is mbsync's historical style)
(Default: unset; will error out when sub-folders are encountered)
IMAP4 Accounts
IMAPAccount name
Define the IMAP4 Account name, opening a section for its parameters.
Host host
Specify the DNS name or IP address of the IMAP server.
If Tunnel is used, this setting is needed only if SSLType is not None and CertificateFile is not
used, in which case the host name is used for certificate subject verification.
Port port
Specify the TCP port number of the IMAP server. (Default: 143 for IMAP, 993 for IMAPS)
If Tunnel is used, this setting is ignored.
Timeout timeout
Specify the connect and data timeout for the IMAP server in seconds. Zero means unlimited.
(Default: 20)
User username
Specify the login name on the IMAP server.
UserCmd [+]command
Specify a shell command to obtain a user rather than specifying a user directly. This allows you
to script retrieving user names.
The command must produce exactly one line on stdout; the trailing newline is optional. Prepend +
to the command to indicate that it produces TTY output (e.g., a prompt); failure to do so will
merely produce messier output. Remember to backslash-escape double quotes and backslashes
embedded into the command.
Pass password
Specify the password for username on the IMAP server. Note that this option is not required. If
neither a password nor a password command is specified in the configuration file, mbsync will
prompt you for a password.
PassCmd [+]command
Specify a shell command to obtain a password rather than specifying a password directly. This
allows you to use password files and agents.
See UserCmd above for details.
UseKeychain yes|no
Whether to use the macOS Keychain to obtain the password. (Default: no)
The neccessary keychain item can be created this way:
security add-internet-password -r imap -s Host -a User -w password [ -T /path/to/mbsync ]
Tunnel command
Specify a command to run to establish a connection rather than opening a TCP socket. This allows
you to run an IMAP session over an SSH tunnel, for example.
AuthMechs type ...
The list of acceptable authentication mechanisms. In addition to the mechanisms listed in the
SASL registry (link below), the legacy IMAP LOGIN mechanism is known. The wildcard * represents
all mechanisms that are deemed secure enough for the current SSLType setting. The actually used
mechanism is the most secure choice from the intersection of this list, the list supplied by the
server, and the installed SASL modules. (Default: *)
SSLType {None|STARTTLS|IMAPS}
Select the connection security/encryption method:
None - no security. This is the default when Tunnel is set, as tunnels are usually secure.
STARTTLS - security is established via the STARTTLS extension after connecting the regular IMAP
port 143. Most servers support this, so it is the default (unless a tunnel is used).
IMAPS - security is established by starting SSL/TLS negotiation right after connecting the secure
IMAP port 993.
SSLVersions [SSLv3] [TLSv1] [TLSv1.1] [TLSv1.2] [TLSv1.3]
Select the acceptable SSL/TLS versions. Use old versions only when the server has problems with
newer ones. (Default: [TLSv1] [TLSv1.1] [TLSv1.2] [TLSv1.3]).
SystemCertificates yes|no
Whether the system's default CA (certificate authority) certificate store should be used to verify
certificate trust chains. Disable this if you want to trust only hand-picked certificates. (De‐
fault: yes)
CertificateFile path
File containing additional X.509 certificates used to verify server identities. It may contain
two types of certificates:
Host These certificates are matched only against the received server certificate itself. They
are always trusted, regardless of validity. A typical use case would be forcing acceptance
of an expired certificate.
These certificates may be obtained using the mbsync-get-cert tool; make sure to verify
their fingerprints before trusting them, or transfer them securely from the server's net‐
work (if it can be trusted beyond the server itself).
CA These certificates are used as trust anchors when building the certificate chain for the
received server certificate. They are used to supplant or supersede the system's trust
store, depending on the SystemCertificates setting; it is not necessary and not recommended
to specify the system's trust store itself here. The trust chains are fully validated.
ClientCertificate path
File containing a client certificate to send to the server. ClientKey should also be specified.
Note that client certificate verification is usually not required, so it is unlikely that you need
this option.
ClientKey path
File containing the private key corresponding to ClientCertificate.
CipherString string
Specify OpenSSL cipher string for connections secured with TLS up to version 1.2 (but not 1.3 and
above). The format is described in ciphers(1). (Default: empty, which implies system wide poli‐
cy).
PipelineDepth depth
Maximum number of IMAP commands which can be simultaneously in flight. Setting this to 1 disables
pipelining. This is mostly a debugging option, but may also be used to limit average bandwidth
consumption (GMail may require this if you have a very fast connection), or to spare flaky servers
like M$ Exchange. (Default: unlimited)
DisableExtension[s] extension ...
Disable the use of specific IMAP extensions. This can be used to work around bugs in servers (and
possibly mbsync itself). (Default: empty)
IMAP Stores
The reference point for relative Paths is whatever the server likes it to be; probably the user's $HOME
or $HOME/Mail on that server. The location of INBOX is up to the server as well and is usually irrele‐
vant.
IMAPStore name
Define the IMAP4 Store name, opening a section for its parameters.
Account account
Specify which IMAP4 Account to use. Instead of defining an Account and referencing it here, it is
also possible to specify all the Account options directly in the Store's section - this makes
sense if an Account is used for one Store only anyway.
UseNamespace yes|no
Selects whether the server's first "personal" NAMESPACE should be prefixed to mailbox names. Dis‐
abling this makes sense for some broken IMAP servers. This option is meaningless if a Path was
specified. (Default: yes)
PathDelimiter delim
Specify the server's hierarchy delimiter. (Default: taken from the server's first "personal"
NAMESPACE)
Do not abuse this to re-interpret the hierarchy. Use Flatten instead.
SubscribedOnly yes|no
Selects whether to synchronize only mailboxes that are subscribed to on the IMAP server. In tech‐
nical terms, if this option is set, mbsync will use the IMAP command LSUB instead of LIST to look
for mailboxes in this Store. This option make sense only in conjunction with Patterns. (Default:
no)
Channels
Channel name
Define the Channel name, opening a section for its parameters.
{Far|Near} :store:[mailbox]
Specify the far resp. near side Store to be connected by this Channel. If Patterns are specified,
mailbox is interpreted as a prefix which is not matched against the patterns, and which is not af‐
fected by mailbox list overrides. Otherwise, if mailbox is omitted, INBOX is assumed.
Pattern[s] [!]pattern ...
Instead of synchronizing only one mailbox pair, synchronize all mailboxes that match the pat‐
tern(s). The mailbox names are the same on the far and near side. Patterns are IMAP4 patterns,
i.e., * matches anything and % matches anything up to the next hierarchy delimiter. Prepending !
to a pattern makes it an exclusion. Multiple patterns can be specified (either by supplying multi‐
ple arguments or by using Pattern multiple times); later matches take precedence.
Note that INBOX is not matched by wildcards, unless it lives under Path.
The mailbox list selected by Patterns can be overridden by a mailbox list in a channel reference
(a Group specification or the command line).
Example: "Patterns % !Trash"
MaxSize size[k|m][b]
Analogous to the homonymous option in the Stores section, but applies equally to Far and Near.
Note that this actually modifies the Stores, so take care not to provide conflicting settings if
you use the Stores in multiple Channels.
MaxMessages count
Sets the maximum number of messages to keep in each near side mailbox. This is useful for mail‐
boxes where you keep a complete archive on the server, but want to mirror only the last messages
(for instance, for mailing lists). The messages that were the first to arrive in the mailbox (in‐
dependently of the actual date of the message) will be deleted first. Messages that are flagged
(marked as important) and (by default) unread messages will not be automatically deleted. If
count is 0, the maximum number of messages is unlimited (Default: 0).
ExpireUnread yes|no
Selects whether unread messages should be affected by MaxMessages. Normally, unread messages are
considered important and thus never expired. This ensures that you never miss new messages even
after an extended absence. However, if your archive contains large amounts of unread messages by
design, treating them as important would practically defeat MaxMessages. In this case you need to
enable this option. (Default: no).
Sync {None|[Pull] [Push] [New] [ReNew] [Delete] [Flags]|All}
Select the synchronization operation(s) to perform:
Pull - propagate changes from far to near side.
Push - propagate changes from near to far side.
New - propagate newly appeared messages.
ReNew - upgrade placeholders to full messages. Useful only with a configured MaxSize.
Delete - propagate message deletions. This applies only to messages that are actually gone, i.e.,
were expunged. The affected messages in the remote Store are marked as deleted only, i.e., they
won't be really deleted until that Store is expunged.
Flags - propagate flag changes. Note that Deleted/Trashed is a flag as well; this is particularly
interesting if you use mutt with the maildir_trash option.
All (--full on the command line) - all of the above. This is the global default.
None (--noop on the command line) - don't propagate anything. Useful if you want to expunge only.
Pull and Push are direction flags, while New, ReNew, Delete and Flags are type flags. The two flag
classes make up a two-dimensional matrix (a table). Its cells are the individual actions to per‐
form. There are two styles of asserting the cells:
In the first style, the flags select entire rows/colums in the matrix. Only the cells which are
selected both horizontally and vertically are asserted. Specifying no flags from a class is like
specifying all flags from this class. For example, "Sync Pull New Flags" will propagate new mes‐
sages and flag changes from the far side to the near side, "Sync New Delete" will propagate mes‐
sage arrivals and deletions both ways, and "Sync Push" will propagate all changes from the near
side to the far side.
In the second style, direction flags are concatenated with type flags; every compound flag immedi‐
ately asserts a cell in the matrix. In addition to at least one compound flag, the individual
flags can be used as well, but as opposed to the first style, they immediately assert all cells in
their respective row/column. For example, "Sync PullNew PullDelete Push" will propagate message
arrivals and deletions from the far side to the near side and any changes from the near side to
the far side. Note that it is not allowed to assert a cell in two ways, e.g. "Sync PullNew Pull"
and "Sync PullNew Delete Push" induce error messages.
Create {None|Far|Near|Both}
Automatically create missing mailboxes [on the far/near side]. Otherwise print an error message
and skip that mailbox pair if a mailbox and the corresponding sync state does not exist. (Global
default: None)
Remove {None|Far|Near|Both}
Propagate mailbox deletions [to the far/near side]. Otherwise print an error message and skip
that mailbox pair if a mailbox does not exist but the corresponding sync state does.
For MailDir mailboxes it is sufficient to delete the cur/ subdirectory to mark them as deleted.
This ensures compatibility with SyncState *.
Note that for safety, non-empty mailboxes are never deleted.
(Global default: None)
Expunge {None|Far|Near|Both}
Permanently remove all messages [on the far/near side] marked for deletion. See RECOMMENDATIONS
below. (Global default: None)
CopyArrivalDate {yes|no}
Selects whether their arrival time should be propagated together with the messages. Enabling this
makes sense in order to keep the time stamp based message sorting intact. Note that IMAP does not
guarantee that the time stamp (termed internal date) is actually the arrival time, but it is usu‐
ally close enough. (Default: no)
Sync, Create, Remove, Expunge, MaxMessages, and CopyArrivalDate can be used before any section for a
global effect. The global settings are overridden by Channel-specific options, which in turn are over‐
ridden by command line switches.
SyncState {*|path}
Set the location of this Channel's synchronization state files. * means that the state should be
saved in a file named .mbsyncstate in the near side mailbox itself; this has the advantage that
you do not need to handle the state file separately if you delete the mailbox, but it works only
with Maildir mailboxes, obviously. Otherwise this is interpreted as a string to prepend to the
near side mailbox name to make up a complete path.
This option can be used outside any section for a global effect. In this case the appended string
is made up according to the pattern :far-store:far-box_:near-store:near-box (see also FieldDelim‐
iter below).
(Global default: ~/.mbsync/).
Groups
Group name [channel[:box[,...]]] ...
Define the Group name, opening a section for its parameters. Note that even though Groups have an
own namespace, they will "hide" Channels with the same name on the command line.
One or more Channels can be specified on the same line.
If you supply one or more boxes to a channel, they will be used instead of what is specified in
the Channel's Patterns. The same can be done on the command line, except that there newlines can
be used as mailbox name separators as well.
Channel[s] channel[:box[,...]] ...
Add the specified channels to the group. This option can be specified multiple times within a
Group.
Global Options
FSync yes|no
Selects whether mbsync performs forced flushing, which determines the level of data safety after
system crashes and power outages. Disabling it is reasonably safe for file systems which are
mounted with data=ordered mode. Enabling it is a wise choice for file systems mounted with da‐
ta=writeback, in particular modern systems like ext4, btrfs and xfs. The performance impact on
older file systems may be disproportionate. (Default: yes)
FieldDelimiter delim
The character to use to delimit fields in the string appended to a global SyncState. mbsync
prefers to use the colon, but this is incompatible with DOS/Windows file systems. This option is
meaningless for SyncState if the latter is *, obviously. However, it also determines the default
of InfoDelimiter. (Global default: ; on Windows, : everywhere else)
BufferLimit size[k|m][b]
The per-Channel, per-direction instantaneous memory usage above which mbsync will refrain from us‐
ing more memory. Note that this is no absolute limit, as even a single message can consume more
memory than this. (Default: 10M)
CONSOLE OUTPUT
If mbsync's output is connected to a console, it will print progress counters by default. The output will
look like this:
C: 1/2 B: 3/4 F: +13/13 *23/42 #0/0 N: +0/7 *0/0 #0/0
This represents the cumulative progress over channels, boxes, and messages affected on the far and near
side, respectively. The message counts represent added messages, messages with updated flags, and
trashed messages, respectively. No attempt is made to calculate the totals in advance, so they grow over
time as more information is gathered.
RECOMMENDATIONS
Make sure your IMAP server does not auto-expunge deleted messages - it is slow, and semantically somewhat
questionable. Specifically, Gmail needs to be configured not to do it.
By default, mbsync will not delete any messages - deletions are propagated by marking the messages as
deleted on the remote store. Once you have verified that your setup works, you will typically want to
set Expunge to Both, so that deletions become effective.
mbsync's built-in trash functionality relies on mbsync doing the expunging of deleted messages. This is
the case when it propagates deletions of previously propagated messages, and the trash is on the target
store (typically your IMAP server).
However, when you intend mbsync to trash messages which were not propagated yet, the MUA must mark the
messages as deleted without expunging them (e.g., Mutt's maildir_trash option). Note that most messages
are propagated a long time before they are deleted, so this is a corner case you probably do not want to
optimize for. This also implies that the TrashNewOnly and TrashRemoteNew options are typically not very
useful.
If your server supports auto-trashing (as Gmail does), it is probably a good idea to rely on that instead
of mbsync's trash functionality. If you do that, and intend to synchronize the trash like other mailbox‐
es, you should not use mbsync's Trash option at all.
Use of the Trash option with M$ Exchange 2013 requires the use of DisableExtension MOVE due to a server
bug.
When using the more efficient default UID mapping scheme, it is important that the MUA renames files when
moving them between Maildir folders. Mutt always does that, while mu4e needs to be configured to do it:
(setq mu4e-change-filenames-when-moving t)
INHERENT PROBLEMS
Changes done after mbsync has retrieved the message list will not be synchronised until the next time mb‐
sync is invoked.
Using Trash on IMAP Stores without the UIDPLUS extension (notably, M$ Exchange up to at least 2010) bears
a race condition: messages will be lost if they are marked as deleted after the message list was re‐
trieved but before the mailbox is expunged. There is no risk as long as the IMAP mailbox is accessed by
only one client (including mbsync) at a time.
FILES
~/.mbsyncrc
Default configuration file
~/.mbsync/
Directory containing synchronization state files
SEE ALSO
mdconvert(1), mutt(1), maildir(5)
Up to date information on mbsync can be found at http://isync.sf.net/
SASL mechanisms are listed at http://www.iana.org/assignments/sasl-mechanisms/sasl-mechanisms.xhtml
AUTHORS
Originally written by Michael R. Elkins, rewritten and currently maintained by Oswald Buddenhagen, con‐
tributions by Theodore Y. Ts'o.
2022 Jun 16 mbsync(1)