Unplugged gnus does not read from mail-sources

[Gerd Boerrigter <gerd.boerrigter@gmx.net>]

Hi,

I have the following setup in my .gnus:

,----[ .gnus ]
| (setq gnus-select-method '(nntp "localhost"))
| 
| ;; methods for reading mail.
| (setq gnus-secondary-select-methods
|       '((nnml "")
|         (nnimap "localhost"
|                 (nnimap-address "localhost")
|                 )
|       ))
| (setq mail-sources
|       '((file)
|         (directory :path "~/Mail/Spool"
|                    :suffix ""
|                    ))
|         )
`----

and also some additional servers configured through the
menus/configure:

,----[ *Server* ]
|      {nnfolder:archive} (opened)
|      {nnimap:mail.external-server.com} (denied)
|      {nndraft:} (opened)
|      {nnimap:localhost} (opened)
|      {nnml:} (opened)
|      {nntp:localhost} (opened)
`----

The only agentized server is the mail.external-server.com, because the
others are local and don't need to be agents.  (BTW, where can I see
if a server is agentized?  They look all alike in the server buffer,
no hint what server is an agent, and who is not.)

If gnus is unplugged, it doesn't get the new mail from the
mail-sources.  Only if I put gnus to plugged mode, the mail from the
mail-sources is read.  Of course, that makes problems with my external
imap server, because I am offline.  Shouldn't an unplugged gnus still
read the mail from the mail-sources and only the agent servers are
treated special?  How can I make that gnus still uses mail-sources,
even if unplugged?  Anything I am overlooking?

Thanks,
Gerd