IMAP folder - cannot delete messages

[Helmut Jarausch <jarausch igpm rwth-aachen de>]

Hi,

I cannot delete nor move any messages from an IMAP (remote) folder.
(though I can using Thunderbird).
>From the right mouse menu, 
Delete Undelete Move to Trash Togle and Move to
are all greyed out.

What am I missing?

Many thanks for a hint,
Helmut.