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isync 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.

Synchronization is based on unique message identifiers (UIDs), so no identification conflicts can occur (as opposed to some other mail synchronizers). Synchronization state is kept in one local text file per mailbox pair; multiple replicas of a mailbox can be maintained.

Note: isync is the name of the project, mbsync is the name of the executable


  • Fine-grained selection of synchronization operations to perform
  • Synchronizes single mailboxes or entire mailbox collections
  • Partial mirrors possible: keep only the latest messages locally
  • Trash functionality: backup messages before removing them
  • IMAP features:
    • Security: supports TLS/SSL via imaps: (port 993) and STARTTLS; CRAM-MD5 for authentication
    • Supports NAMESPACE for simplified configuration
    • Pipelining for maximum speed (currently only partially implemented)


Install isyncAUR from the official repositories or isync-gitAUR can be installed from the AUR.


First create and customize the main configuration file using this example ~/.mbsyncrc:

IMAPAccount gmail
# Address to connect to
Pass ***************
# To store the password in an encrypted file use PassCmd instead of Pass
# PassCmd "gpg2 -q --for-your-eyes-only --no-tty -d ~/.mailpass.gpg"
# Use SSL
UseIMAPS yes
# The following line should work. If get certificate errors, uncomment the two following lines and read the "Troubleshooting" section.
CertificateFile /etc/ssl/certs/ca-certificates.crt
#CertificateFile ~/.cert/
#CertificateFile ~/.cert/Equifax_Secure_CA.pem

IMAPStore gmail-remote
Account gmail

MaildirStore gmail-local
# The trailing "/" is important
Path ~/.mail/gmail/
Inbox ~/.mail/gmail/Inbox

Channel gmail
Master :gmail-remote:
Slave :gmail-local:
# Exclude everything under the internal [Gmail] folder, except the interesting folders
Patterns * ![Gmail]* "[Gmail]/Sent Mail" "[Gmail]/Starred" "[Gmail]/All Mail"
# Or include everything
#Patterns *
# Automatically create missing mailboxes, both locally and on the server
Create Both
# Save the synchronization state files in the relevant directory
SyncState *

To get rid of the [Gmail]-Stuff (or [Google Mail] as in my case) in each mailbox name, it's possible to use separate Channels for each directory, and later merge them to a group:

Channel sync-googlemail-default
Master :googlemail-remote:
Slave :googlemail-local:
# Select some mailboxes to sync
Patterns "INBOX" "arch"

Channel sync-googlemail-sent
Master :googlemail-remote:"[Google Mail]/Gesendet"
Slave :googlemail-local:sent

Channel sync-googlemail-trash
Master :googlemail-remote:"[Google Mail]/Papierkorb"
Slave :googlemail-local:trash

# Get all the channels together into a group.
Group googlemail
Channel sync-googlemail-default
Channel sync-googlemail-sent
Channel sync-googlemail-trash

As you can see, name-translations are possible this way, as well. Now calling

mbsync googlemail

will sync all the folders.


First make any folders that were specified as Maildirs.

$ mkdir -p ~/.mail/gmail

Then to retrieve the mail for a specific channel run:

$ mbsync gmail

or to retrive the mail for all channels:

$ mbsync -a


If you get certificate related errors, you may need to retrieve the server's certificates manually in order for mbsync to correctly verify it.

Step #1: Get the certificates

Tango-inaccurate.pngThe factual accuracy of this article or section is disputed.Tango-inaccurate.png

Reason: This may not always be needed, e.g. for gmail CertificateFile /etc/ssl/certs/ca-certificates.crt in the config file may be suffcient (Discuss in Talk:Isync#Step #1: Get the certificates)

$ mkdir ~/.cert
$ openssl s_client -connect some.imap.server:port -showcerts 2>&1 < /dev/null | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' | sed -ne '1,/-END CERTIFICATE-/p' > ~/.cert/some.imap.server.pem

This will create a certificate file called ~/.cert/some.imap.server.pem (e.g. ~/.cert/ If you wish to do this manually, you may enter:

$ openssl s_client -connect some.imap.server:port -showcerts

and it will display output something like:

depth=1 C = US, O = Google Inc, CN = Google Internet Authority
verify error:num=20:unable to get local issuer certificate
verify return:0
Certificate chain
 0 s:/C=US/ST=California/L=Mountain View/O=Google Inc/
   i:/C=US/O=Google Inc/CN=Google Internet Authority
 1 s:/C=US/O=Google Inc/CN=Google Internet Authority
   i:/C=US/O=Equifax/OU=Equifax Secure Certificate Authority
Server certificate
subject=/C=US/ST=California/L=Mountain View/O=Google Inc/
issuer=/C=US/O=Google Inc/CN=Google Internet Authority
No client certificate CA names sent
SSL handshake has read 2108 bytes and written 350 bytes
New, TLSv1/SSLv3, Cipher is ECDHE-RSA-RC4-SHA
Server public key is 1024 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
    Protocol  : TLSv1.1
    Cipher    : ECDHE-RSA-RC4-SHA
    Session-ID: 77136647F42633D82DEDFBB9EB62AB516547A3697D83BD1884726034613C1C09
    Master-Key: 635957FBA0762B10694560488905F73BDD2DB674C41970542ED079446F27234E2CA51CF26938B8CA56DF5BBC71E429A7
    Key-Arg   : None
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    TLS session ticket lifetime hint: 100800 (seconds)
    TLS session ticket:
    0000 - d6 5b a0 a7 10 0e 64 04-72 93 7c 9f 94 fa 07 57   .[....d.r.|....W
    0010 - f1 8b 9d 24 8b 9d 1b f3-a8 b1 4d 2c a9 00 e1 82   ...$......M,....
    0020 - 00 83 1e 3f e5 f2 b2 2c-d2 a8 87 83 16 02 0d 1e   ...?...,........
    0030 - bf b6 c1 d6 75 21 04 e6-63 6b ab 5b ed 94 7a 30   ....u![..z0
    0040 - 1a d0 aa 44 c2 04 9b 10-06 28 b5 7b a0 43 a6 0d   ...D.....(.{.C..
    0050 - 3b 4a 85 1f 2e 07 0a e1-32 9b bd 5d 65 41 4c e2   ;J......2..]eAL.
    0060 - 7c d7 43 ec c4 18 77 53-b5 d4 84 b4 c9 bd 51 d6   |.C...wS......Q.
    0070 - 2d 4f 2e 10 a6 ed 38 c5-8e 9d f8 8b 8a 63 3f 7b   -O....8......c?{
    0080 - ee e6 b8 bf 7a f8 b8 e8-47 92 84 f1 9b 0c 63 30   ....z...G.....c0
    0090 - 76 d8 e1 44                                       v..D

    Start Time: 1352632558
    Timeout   : 300 (sec)
    Verify return code: 20 (unable to get local issuer certificate)
* OK Gimap ready for requests from o67if11168976yhc.67

Simply copy the first block that begins with -----BEGIN CERTIFICATE----- and ends with -----END CERTIFICATE-----, paste into a file, and save with a .pem extension (this is necessary for the next step). Older instructions state that, with Gmail, both certificate blocks must be saved but on testing this was found to be unnecessary.

Now, copy the root issuer certificate to your local certificate folder. In this example (Gmail), the root issuer is Equifax Secure Certificate Authority. This certificate is included in the ca-certificates package.

cp /usr/share/ca-certificates/mozilla/Equifax_Secure_CA.crt ~/.cert/Equifax_Secure_CA.pem

Step #2: Rehash the certificates

$ c_rehash ~/.cert

Sample Output:

Doing  ~/.cert/
some.imap.server.pem => 1d97af50.0
Equifax_Secure_CA.pem => 28def021.3

This creates a symlink to the certificate file named with a cryptographic hash of its contents.

Exchange 2003

When connecting to an MS Exchange 2003 server, there could be problems when using pipelining (i.e. executing multiple imap commands concurrently). Such an issue could look as follows:

sample output of `mbsync -V exchange'

>>> 9 SELECT "arch"^M
* 250 EXISTS
* FLAGS (\Seen \Answered \Flagged \Deleted \Draft $MDNSent)
* OK [PERMANENTFLAGS (\Seen \Answered \Flagged \Deleted \Draft $MDNSent)] Permanent flags
* OK [UNSEEN 241] Is the first unseen message
9 OK [READ-WRITE] SELECT completed.
>>> 10 UID FETCH 1:1000000000 (UID FLAGS)^M
* 1 FETCH (UID 1 FLAGS (\Seen \Answered))
* 2 FETCH (UID 2 FLAGS (\Seen \Answered))
* 249 FETCH (UID 696 FLAGS ())
* 250 FETCH (UID 697 FLAGS (\Seen))
10 OK FETCH completed.
>>> 11 APPEND "arch" (\Seen) {4878+}^M
(1 in progress) >>> 12 UID FETCH 697 (BODY.PEEK[])^M
(2 in progress) >>> 13 UID STORE 696 +FLAGS.SILENT (\Deleted)^M
12 BAD Command is not valid in this state.

So command 9 is to select a new folder, command 10 checks the mail and commands 11, 12 and 13 run in parallel, writing/getting/flagging a mail. In this case, the Exchange server would terminate the connection after the BAD return value and go on to the next channel. (And if all went well in this channel, mbsync would return with 0.) After setting

PipelineDepth 1

in the IMAPStore config part of the Exchange, this problem did not occur any more.

External Links