@olaf7 The synchronization issue is pretty strange and I don't reproduce it...
About offlineimap settings, once you have enabled the feature, you need to create at least one provider (gmail.com for example) where you'll be able to fill-in connection parameters and more.

As in editing the almost empty config file provided by hand to suit my needs? Or will I be able to edit and or select anything from Modoboa/GUI once the config file is provided with a provider? A webform to supply details/parameters would be nice as now the configfile is not much more than a placeholder/marker.
As you can see my generated config file is far off from the template as provided by https://github.com/modoboa/modoboa/blob/master/modoboa/imap_migration/templates/imap_migration/offlineimap.conf

Have you defined a provider and a migration yet?

Please note: effectively this issue should be split into two issues imho. My bad. 1. mismatch settings v1/v2 and 2. IMAP migration
Also: can you comment on how I can help debug this as clearly something is wrong (as can be seen by screenshots), but you cannot reproduce.

To answer your question regarding the imap_sync issue: I created a .offlineimaprc based on the template, but it fails for a couple of reasons:

1. IIRC no domain and accounts should be created in advance. There is no existing domain, so no domain admin. Therefor I need to use Modoboa Administrator. This user has no postbox, so no Dovecot login, so offlineimap fails.
2. You do not know upfront what the remote IMAP server type is and what configuration is supported / what tweaking is required. Obviously I know what the server is in my case, but in general this is an issue. Settings can currently not be tweaked from within Modoboa.

After creation of the file nothing has changed to the GUI, so the screenshots provided here are still as it is. So editing is not possible. I assume this is by design?

Also note (more an OfflineIMAP issue, and something not easily to be avoided): passwords will be stored unencrypted in a file on disk.

Please create another issue for the sync issue and keep this one for generation.