If the mailbox name is suffixed with the server's hierarchy
delimiter, this indicates to the server that the client intends to
create mailbox names under the specified name in the hierarchy. If
superior hierarchical names are specified in the mailbox name, then
the server may automatically create them as needed. For example, if
the mailbox name "Mail/Office/Projects" is specified and
"Mail/Office" does not exist, it may be automatically
created by the server.
The special mailbox name INBOX is reserved, and cannot be created.
It is recommended that mailbox names only consist of printable ASCII
characters, and the special characters "*" and
"%" should be avoided.