Imapsync tutorial

$Id: TUTORIAL_Unix.t2t,v 1.27 2022/01/14 12:42:51 gilles Exp gilles $

1. Good practices overview

2. Basic steps

2.1. Verifying imapsync works well

Open a terminal and go to the imapsync directory. The imapsync directory is the directory created by the extraction of the tarball (.tgz), its name is where is imapsync release number (2.178 at the time of this proofread).


Verify imapsync runs on your system


It should output the help message.

If the previous command fails then there is an installation issue. Go back to the section, then read and apply the installation file corresponding to your system and drop me an email about your issue.

Next, verify imapsync runs well with live tests. This check needs Internet access. It does a simple sync between two real dedicated imap mailboxes located at the host

  ./imapsync --testslive

Now verify that the script examples/ runs fine:

  sh examples/

This script does the same thing as "imapsync --testslive" but it uses explicitly the 6 parameters so it will be a good start for your future own script.

2.2. Working with your data

I consider you're still in the imapsync top directory.

Make a copy of the script examples/

  cp examples/   mysync

Check that the copy works as the original

  sh mysync

So far so good, now we're going to work with your data.

2.3. Prepare your credentials

An IMAP account is accessed with 3 parameters,

Since imapsync job is to sync two imap accounts, we need 3 + 3 = 6 parameters:

2.4. Take a real user account as a source

Even during the learning time with imapsync, you can take a real user account as a source. There is also no problem if this account is currently used by a user. By default, this account will only be read, no change will be made by imapsync on it. It's safe to use a normal and live account as a source, even to learn imapsync.

Assuming that the imap source server name host1 is, the user1 account name is myuser1 and its password is mysecret1, we now have the first three parameters.

2.5. Take a test user account as a destination

Unlike the source side, the destination side will be modified by imapsync. Therefore, for learning, checking, and adjusting, it is not a good idea to use a real user imap account the first time you play with imapsync.

If you really can't afford a test account on host2, it's ok, imapsync is not that bad but you may have some work to do to fix some unwanted behavior. Unwanted behavior is mostly folders names that you don't want to be the same on both sides.

Assuming that the imap destination server name host2 is, the user2 account name is myuser2 and its password is mysecret2, we now have the next three parameters.

2.6. Edit your own script mysync

Now edit the script mysync and replace the test values with yours.

You're ready for a dry test on your accounts.

  sh mysync

Since the mysync script is a copy of examples/, your first run with your data should include three other options --automap --justfolders --dry. With --dry option, nothing will be done for real on host2 but yet it will test whether the credentials are ok on both sides. You'll encounter two successful logins, or one login failure on host1 or host2, or two failures on host1 and host2. If the logins are ok, you will be able to observe that the folders mapping is ok.

If login fails then double-check all three values that identify the account, which are the host, the login name, and the password.

If the folders mapping proposed is not ok then you can fix it with the option --f1f2. The following example maps the source folder "Sent Messages" to the destination folder "Sent". The double-quotes are not part of the names of the folders but they should be used when special characters like blanks are in the names of the folders:

  ./imapsync ...  --f1f2 "Sent Messages=Sent"

As explained in the inline help or the README:

  --f1f2    str1=str2 : Force folder str1 to be synced to str2.

You're ready for a real test on your accounts, restricted to folders. Remove --dry from the mysync script and rerun mysync:

  sh mysync

3. Background knowledge about mailboxes

Three Internet protocols are used to access almost all email accounts: POP3, IMAP, HTTP.

The oldest protocol still used to access mailboxes is POP3, the Post Office Protocol. POP3 gives access to only one main box called INBOX.

With POP3, messages have no flags at all, no Seen/UnSeen, Forwarded, or Flagged labels.

It's not systematic but messages are often removed from a POP3 server each time a software client looks into it, so messages only appear on the client host that fetched them, they are unavailable from any other system located elsewhere.

The second protocol to deal with email messages is IMAP, Internet Message Access Protocol. IMAP gives access to a hierarchy of mailboxes also called folders. Other IMAP features are concurrent accesses, tagging with flags, search by many criteriums like date, subject, size, etc.

The IMAP protocol presents most of the features POP lacks. Messages stay on the imap server so any client on the network can access them at any time from anywhere, the same messages with the same flags.

The third protocol to access email messages is HTTP, HyperText Transfer Protocol. HTTP is the protocol to browse the web.

Web browsers like Google Chrome, Mozilla Firefox, Internet Explorer and Safari are HTTP client software tools. You already know that so what's the point with HTTP mailboxes? HTTP mailboxes are called webmails. Webmails often offer the same features as imap servers because webmails underlying storage systems are often imap servers.

Webmails systems like Gmail, Yahoo, Exchange, Zimbra, or Office365 are also accessible via imap.

The conclusion of this protocol review is that mailboxes can be accessed using the IMAP protocol, most of the time. Here comes imapsync.

In case the source mailbox is only accessible by the POP protocol, you can use the tool pop2imap to sync them. pop2imap is located at

4. Imapsync presentation

Software imapsync is a command-line tool to copy, migrate, backup, or synchronize IMAP mailboxes.

Command line means imapsync is not graphical, it is textual. Usually, with command-line tools, you have to type characters on your keyboard. But your fingers won't suffer much pain typing on the keyboard because script examples are given, nearly ready to run. Most of the time you only have to change the main values in those files and adapt them to your context.

Don't be afraid, the mouse won't be forsaken. You can still use the mouse to launch an editor, select/copy/paste complete examples, and run the little script with a double-click.

Imapsync runs on Linux, Windows, and OS X (Macintosh/Darwin world). Imapsync is written in the Perl language and, thanks to the Perl developers, Perl runs mostly everywhere. So does imapsync.

While operating systems have a lot in common, they sometimes differ, especially within their syntax. I won't blame anyone, historically Windows came after Unix. The marvelous designers in these old times decided it would be very cool to not share the same syntax for doing the same things.

To designate an end of the line, Unix uses the character \n Windows uses two characters \r\n and Mac use \r. Thanks to you guys, great thinking! Fifty years later, we still suffer from this...daily.

To avoid some headaches with systems that no one masters I will give examples in both worlds, Unix and Windows. OS X users are in the Unix world nowadays so they must follow the Unix examples.

5. Conventions

To simplify display or print, each imapsync command line is usually written in several lines but it could be written in one single line.

If you prefer to use the whole command written in one single line then just remove the last visible character of each line ( \ or ^ ) and also the carriage return character. The last visible character \ or ^ means "command continues on next line"; it's the backslash \ character on Unix and the caret ^ character on Windows.

For example, on Unix, a command like the following:

    imapsync \
       --host1 \
       --user1 test1 \
       --password1 secret1 \

is equivalent to:

    imapsync --host1 --user1 test1 --password1 secret1 ...

and on Windows, a command like the following:

    imapsync.exe ^
       --host1 ^
       --user1 test1 ^
       --password1 secret1 ^

is equivalent to:

    imapsync --host1 --user1 test1 --password1 secret1 ...

6. Why start with a test account on destination host2?

A little explanation about this hint. Imapsync is safe with accounts on host1, it doesn't change anything on them, it just read them. The exception of this safe principle is when --delete1 option is used, since --delete1 removes on host1 each message successfully copied to host2, messages that couldn't be transferred stay on host1.

It's not the same for destination accounts as imapsync writes on host2 accounts. Imapsync creates folders on them, adds messages, and sets flags on messages. It isn't safe on a real account. So don't use a real user account to test imapsync. Learn to use it and see what it does on a test account at host2.

What can badly happen? The most common bad behavior is that folders mapping won't be what you expect because it is strictly reproduced from host1 to host2. The second bad behavior is getting duplicates on the second run and after; it's rare but it can happen when an imap server software changes the headers "Message-Id" or "Received". Solutions to avoid duplicates are often easy (There's a FAQ called FAQ.Duplicates.txt about that). It's also possible to remove the duplicates on host2 but it's better to avoid them on user accounts at first, users won't like that you mess up their mailboxes.

7. Imapsync default behavior

By default, unless explicitly told to do something else:

8. To go further with imapsync

Imapsync has many options but you can ignore most of them and still make great transfers.