[VM] imap-fcc and gmail

[emacs user]

hi all,

This has been asked before, and I looked at the manual, but still could not 
figure it out:  adding 
imap-fcc: Sent
or 
imap-fcc: Sent Mail

the mail appears in gmail under a label such as 
[imap] Sent
rather then in the Sent mail label/ folder.

any hints?  

BTW, the manual on IMAP-FCC did not seem to say *how* to add this field 
automatically.  I eventually found mail-default-headers, but perhaps it would 
be good to mention it explicitly?

thanks, E