Sami is correct. imapsync loses data.

Source -> imapsync -> destination : the mailboxes are different to an IMAP client

Source -> dsync -> destination (running Dovecot w/doveadm): the mailboxes are the same

You may not care that your users w/100,000 message mailboxes that have been cached on their client now have to invalidate that entire cache (and most likely re-download all of those messages).

So there is zero argument that, due to IMAP metadata loss, this is something that doesn't happen if dsync (or rsync) is used.

michael

On September 4, 2018 at 9:45 AM Rick Romero <rick@havokmon.com> wrote:

Quoting Robert Schetterer <rs@sys4.de>:

Am 04.09.2018 um 17:18 schrieb Sami Ketola:

On 4 Sep 2018, at 18.00, Robert Schetterer <rs@sys4.de> wrote:

Am 04.09.2018 um 16:52 schrieb Sami Ketola:

On 4 Sep 2018, at 17.47, Robert Schetterer <rs@sys4.de> wrote:

Am 04.09.2018 um 09:41 schrieb Sami Ketola:

imapsync always loses data

never saw this, be carefull by anounce such myths
It is a fact. Imapsync works over IMAP only and IMAP protocol does not even support transferring all data. At most at least UID numbering will be lost and end users need to invalidate their local caches.
but using "looses data" might others think it also may fail with imap,
so be more detailed next time
UID number is also data that is saved on the IMAP backend. If that is lost then it's "lost data".

Sami
Sorry i migrated terrabytes of mail with imapsync and never had a
problem, it works as designed, also with maildir rsync did a good job,
what never worked as it should was dsync ,cause of bugs ,that may
changed now

so this is my answer to topic

"Best way to move mail from one server to another"

https://imapsync.lamiral.info/FAQ.d/FAQ.Duplicates.txt

Seems to use UIDs so that 'data' isn't lost.