[Dovecot] Disallow certain characters in foldernames?

[Charles Marcus]

Is there a way to do this in dovecot? Similar to how you can

When using Maildir and Thunderbird, if a user tries to a create folder 
named "test.1" or "test/1", dovecot will happily create a folder called 
"test", with a subfolder called "1".

Worse, the top level folder "test" is greyed out, which is how 
Thunderbird displays a folder that can contain only other folders, not 
both folders and files.

I want to disallow this. Obviously I'd prefer if Thunderbird would 
display a meaningful error, but most likely dovecot cannot control that.

I don't really care if the user just gets some kind of weird generic 
error or not, I'd just prefer to prevent dovecot from creating the 
problematic folders, and explain the problem to the user if/when they 
call about it (after NOT reading my carefully crafted documentation 
explaining the illegal characters that cannot be used in foldernames).

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Best regards,

Charles