> On 21/10/2025 04:29 EEST rmfuhrer--- via dovecot <[email protected]> wrote:
> 
>  
> I'm trying to use dsync to upgrade from an existing 2.3 server running native 
> on MacOS to a 2.4.1 server running inside a Docker container on the same 
> machine, using the official Dovecot 2.4.1 Docker image from DockerHub.
> 
> For testing, I decided to set up a new hostname (CNAME) record in DNS 
> pointing to the same IP, since both Dovecot instances are running on the same 
> host.
> 
> The new 2.4.1 Docker-containerized instance is working fine so far, which is 
> to say I can connect to it from a mail client (the Mac Mail app) using 
> TLS/SSL, and I'm able to move mail messages in, delete them, create folders, 
> etc.
> 
> For the next phase of testing, I want to migrate a single folder of a single 
> user's email from the 2.3 instance to the new 2.4.1 Docker instance. I 
> recently found out about dsync and thought I'd give it a try.
> 
> The test Dockerized instance exposes its IMAPS port to a different port than 
> the legacy instance (of course).
> 
> I found that dsync seems to behave differently than the IMAP service wrt the 
> certficate chain: Whereas the Mail client was able to negotiate the encrypted 
> connection with the LetsEncrypt server cert alone in the dovecot cert file, 
> with dsync, the 2.3 server seemed to require the entire cert chain to reside 
> in the file. (?)
> 
> After resolving that, the source dsync could at least get past the 
> certificate validation phase, but then complained thusly:
> 
> Oct 19 21:52:11 doveadm([email protected]): Error: doveadm server sent 
> invalid handshake: * OK [CAPABILITY IMAP4rev1 LOGIN-REFERRALS ID ENABLE IDLE 
> SASL-IR LITERAL+ AUTH=PLAIN AUTH=LOGIN] Dovecot ready.
> Oct 19 21:52:11 doveadm([email protected]): Error: Disconnected from 
> remote: EOF
> Oct 19 21:52:11 doveadm([email protected]): Debug: auth-master: conn 
> unix:/usr/local/var/run/dovecot/auth-userdb (uid=0): Disconnected: Connection 
> closed (fd=8)
> 
> I can't tell from that error message what the source dsync doesn't like about 
> the destination dsync, or for that matter, whether it might be the 
> destination dsync that doesn't like what the source dsync is saying??
> 
> Anyway, I'm invoking dsync like this, to sync just a single folder:
> 
> $ sudo doveadm -D -v backup -u [email protected] -m FolderName 
> tcps:testserver.mydomain.net:31993
> 
> ALSO: I confess that I also don't understand how dsync can work without 
> asking for user account passwords, if it's indeed running over the IMAPS 
> service. How can the destination service trust the incoming dsync connection? 
> I assume it's running over a normal IMAPS connection, since that's the only 
> port that I've given to the source dsync command, but maybe that's not the 
> case?
> 
> The docs are pretty unclear about this aspect, but I'm no expert, so maybe 
> this is just obvious to others. (?)

Hi!

Please look at migration guide at 
https://doc.dovecot.org/2.4.1/core/admin/migration.html

Aki

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