Dovecot UIDs and POP.

[Sami Ketola]

> On 25 Sep 2019, at 15.14, Ionel via dovecot <dovecot at dovecot.org> wrote:
> 
> 
> 
> On 25.09.19 12:29, Sami Ketola via dovecot wrote:
>> 
>> 
>>> On 25 Sep 2019, at 4.52, Plutocrat via dovecot <dovecot at dovecot.org> wrote:
>>> 
>>> On 24/09/2019 10:14 PM, @lbutlr via dovecot wrote:
>>>> Did the target machine already have the user setup? I think dsync wants to sync mailboxes between configured and working servers with users already defined.
>>> 
>>> Yes, of course. And the directory structure was pretty much identical between the two. Which was how I was able to write and run the rsync script. 
>>> 
>>> I think at this point, I'm past the dsync problems. That window has closed, and the migration is done, albeit with this irritating re-downloading of email with POP problem. However I'm still keen to get to the bottom of how this whole UID/UIDL/POP3 transaction takes place, so I can understand it for the future, and prevent it happening again. I'm guessing it would be a useful addition to the dovecot documentation as well. 
>> 
>> If you want to keep the data complete then the only proper way to do the migration is dsync. Specially since you now were migrating dovecot to dovecot.
>> 
>> imapsync does not retain imap uids or pop3 uidls. all users would need to clear their local caches.
>> 
>> Sami
>> 
> Very interesting thread, since I was about to perform the migration in
> the next few days. I was operating under the assumption that imapsync
> would retain both imap uids and pop3 uidls. According to Sami's post
> this is not the case. This begs the question which path to take. The
> source server is dovecot, albeit a very old version with no dsync (we're
> talking dovecot 1.x.x).
> 
> Any ideas?
> 


Native doveadm protocol between two major versions might not be compatible so I would not use that.
What I would do in your case is to use imapc connector to pull the emails with dovecot dsync and pop3_migration -plugin
to fetch the POP3 UIDLs from the old server over pop3 connection.

https://wiki2.dovecot.org/Migration/Dsync

Sami