New mailbox not getting created in new macOS 10.12.1 After I had migrated to 10.12.1, I started facing issues in creating new mailboxes in my mail account in the official Mail app. Earlier, I simply used to create a new mailbox and it used to appear immediately on the left-hand side along with other mailboxes. But now, when I create a mailbox, it asks me the Location and Name, and then nothing happens. Nowhere the mailbox is and I have a tough time to find a solution of this.

I tried creating a new folder in my email account by logging into the web interface (Squirrelmail), and it showed up as a new mailbox, but the reverse is not working.

Is this a known issue in 10.12.1? Any workaround / fix for this? I am having my own domain and using IMAP to configure the same in Mail app.

Thanks.
I was having this issue as well, but stumbled across the answer, at least on my system. In the Mailboxes sidebar, try hovering over the name of the Mailbox within which you've tried to create new mailboxes...you should see a '+' as well as a 'Show' option appear to the right of the Mailbox name. Click 'Show' (not the '+'). The sub-mailboxes you've created should now appear beneath the main Mailbox.