One way to use Gnus to read (part of one's) mail is to configure it to collaborate with procmail. For this purpose, you have to instruct procmail to save the selected mail into specific spool folders, which Gnus will use as input. The related settings (in your ~/.emacs) may look like:
(setq mail-sources '((directory :path "~/mail/" :suffix ".spool")))and in your ~/.procmailrc:
:0: * ^TOeveryone@shire\.ntc\.nokia\.com mail/everyone.spool