dovecot - Dec 2019 - Is it safe to mix dovecot import/backup/sync between dovecot versions 2.2.30.2 and 2.3.7.1?

I am migrating a server. The old one uses dovecot 2.2.30.2 and the new one
2.3.7.1. I don?t want to use any tool that might influence flags on messages. I
am using Maildir format on both ends and I have a way to let one server access
the data on the other (either using an rsync or a direct access).

Could I set up a sync between both to create a smooth migration?

Gerben Wierda
Chess and the Art of Enterprise Architecture <http://enterprisechess.com/>
Mastering ArchiMate <http://masteringarchimate.com/>
Architecture for Real Enterprises
<https://www.infoworld.com/blog/architecture-for-real-enterprises/> at
InfoWorld
On Slippery Ice <https://eapj.org/on-slippery-ice/> at EAPJ

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> On 22 Dec 2019, at 12.22, Gerben Wierda <gerben.wierda at rna.nl>
wrote:
> 
> I am migrating a server. The old one uses dovecot 2.2.30.2 and the new one
2.3.7.1. I don?t want to use any tool that might influence flags on messages. I
am using Maildir format on both ends and I have a way to let one server access
the data on the other (either using an rsync or a direct access).
> 
> Could I set up a sync between both to create a smooth migration?
rsync probably works out fine, but I would use native dovecot dsync myself. 

Something like this run on the new server:

/usr/bin/doveadm backup -u <userid> -R ssh adminuser at old-server
"sudo /usr/bin/doveadm dsync-server -u <olduserid>"

Sami

Thank you.
> On 22 Dec 2019, at 12:36, Sami Ketola <sami.ketola at dovecot.fi>
wrote:
> 
> 
>> On 22 Dec 2019, at 12.22, Gerben Wierda <gerben.wierda at rna.nl>
wrote:
>> 
>> I am migrating a server. The old one uses dovecot 2.2.30.2 and the new
one 2.3.7.1. I don?t want to use any tool that might influence flags on
messages. I am using Maildir format on both ends and I have a way to let one
server access the data on the other (either using an rsync or a direct access).
>> 
>> Could I set up a sync between both to create a smooth migration?
> 
> rsync probably works out fine, but I would use native dovecot dsync myself.
So just for certainty: I canjust perfectly copy over the 2.2.30 Maildir to the
new server for each user and dovecot 2.3.7 would just work? No need to do
anything else, such as recreating indexes etc? That would probably be perfect
for me.
> 
> Something like this run on the new server:
> 
> /usr/bin/doveadm backup -u <userid> -R ssh adminuser at old-server
"sudo /usr/bin/doveadm dsync-server -u <olduserid>?
For this I would have to create the ssh-setup for adminuser which I?re rather
prevent to have to do, because the _dovecot user doesn?t have a login shell etc.
and the servers are rather closed down with respect to ssh etc for security
reasons.

I have to admit I haven't really had to administer dovecot before (macOS
Server was doing that for me) so I?m quite overwhelmed with all the settings,
options, configurations and workings.

It would be nice to have something like this in a crontab of the *old* server:

	doveadm sync remote:server-replica.example.com

but I have no idea what I have to do in terms of getting this to work safely.
Probably set up a master user on the new server?s end? Since all instructions I
can find are based on some sort of Linux (and my servers are macOS) I have no
idea yet what to do *exactly*. There are also no imapc entries yet on both
servers in the config. User database on macOS is different as far as I know
(LDAP: Open DIrectory). I am running into not understanding this, for instance
from the Wiki:
# Authenticate as masteruser / masteruser-secret, but use a separate login user.
# If you don't have a master user, remove the imapc_master_user setting.
imapc_user = %u
imapc_master_user = masteruser
imapc_password = masteruser-secret
And that leaves me wondering: what does "imapc_user = %u" do exactly?
Can I use any existing local user to run the doveadm commands and will the %u
become the user name of that user for instance?

I other words, I?m drowning in details and a simple copy of the mail directories
would be a perfect solution.

G
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