[Dovecot] Drafts, Trash, Sent

[libero1]

Hi,
I'm testing a dovecot installation using thunderbird as imap client.
The first user I configured has regolar folders: Drafts, Sent and Trash, and thunderbirs shows each one with its icon.
The second user shows these folders with a standard icon, and I'm not able to save email in sent.

I cann't understand why there is this difference, and how dovecot manage these folder.
Can anyone help me?

Thanks a lot
Roger