Why isn't my Outlook folder synced to the IMAP server?

Question

I want to migrate all my emails from one IMAP server to another. Therefore I added both accounts to Outlook 2013, created a folder underneath the new account and copied all mails from my old account in this folder.

Afterwards Outlook showed a progress bar for several hours in its status bar. However, the created folder isn't visible in other IMAP clients nor in the web client (zimbra planetary mail).

Was the folder synced to the server at all? How to display it in other clients?

Answer 1

File > Account Settings > Select your IMAP account > Change > adjust the "Mail to keep offline" to "All", then check the result.

Failing this, I just did a bit of googling, and there seem to be a lot of people having problems with syncing from IMAP to IMAP. The generally offered (and accepted) solution appears to be to export the old mailbox to PST/PSTX and then import it into your new imap store.