plus addressing to a mailbox with a space in its name

[Jon Rowell]

I want to be able to use plus addressing to send email directly to a  
user's mailbox.  Here's an example:

jondoe+test mailbox at myserver.com

Where 'test mailbox' (with a space and without the quotes) is a mail  
folder in jondoe's inbox.  I've tried several variations:

jondoe+test\ mailbox at myserver.com
jondoe+test\\\ mailbox at myserver.com

And quite a few other ones that are definitely wrong.

Has anyone had success with using plus addressing to send to a  
specific mail folder when the folder name has a space in it?

Jon Rowell