By selecting Settings, a new page will appear with a left side menu.

1. IMAP MAILBOX – you can manage the IMAP accounts. Every IMAP account has separated training data. You can delete an account by clicking on the bin icon or add new ones by clicking on the Add new button.

To see more details about configurating a new account go to Configure Email Account.
If there is only one account registered it cannot be deleted but it can be modified.
The default IMAP MAILBOX is the one with the ID = 1.