> On 5 Dec 2017, at 12.46, Webert de Souza Lima <webert.b...@gmail.com> wrote:
> Sorry, I might be wrong about cache invalidation, indeed. What I'm sure is
> that users will hardly notice any server change.
> We've never had user complaints about mailboxes resyncing or anything like
> that after imapsync'ing to a new server, that's why I'd recommend using
> imapsync with no worries.
> It's easy enough to test this on a single user account first and see how is
> imap client's behavior after the DNS change.

Can't really do DNS change to test with one user as DNS change affects all 
users. What we usually
do is put layer of dovecot proxies in front of the legacy and destination 
platform and then have database
with information if user has been migrated already and forward the connection 
to legacy or dovecot
platform based on that info. That enables us to migrate user-by-user.

And both users and mail server admins do notice if there is IMAP UID or POP3 
UIDL changes. Imagine
what happens when millions of users suddenly start to redownload terabytes of 


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