It's not possible to create folder which name starts with hash-sign (#)

Hi,
I ran into an issue when importing mails from other servers - it seems that it's not possible to 
create folder which name starts with hash-sign, e.g.: "#testfolder".

I tested other mail servers (gmail, mailu [postfix?], fastmail [cyrrus?], mailbox.org, infomaniak 
[no idea what they use]) and all of them allowed folder names starting with "#".


```
A4 CREATE #hashtest
A4 NO CREATE You can not access a mailbox that does not belong to you
```

Looking at the spec (https://datatracker.ietf.org/doc/html/rfc3501#section-5.1) it seems that `#` 
can have special meaning and could be used to denote namespaces.

Is it a configurable option (i.e. is it possible to disable namespaces/shared mailboxes or some 
such) that would result in James allowing mailboxes starting with `#`?

-- 
Wojtek