1. Make sure you’ve set up Postfix or some other mail server that can send mail.
2. Install dovecot (IMAP server) and offlineimap (IMAP synchronization). You can probably find binaries for your distribution.
3. Edit /etc/dovecot/conf.d/10-mail.conf and set the following:

   mail_location = maildir:~/Maildir:LAYOUT=fs

4. Use the instructions from http://unix.stackexchange.com/questions/44214/encrypt-offlineimap-password to set up GPG-encrypted passwords. (optional)
5. Put the following in ~/.offlineimaprc, changing the details as needed.

   [general]
   accounts = SachaGmail
   pythonfile = ~/bin/offlineimap-password.py
   
   [Account SachaGmail]
   localrepository = Local
   remoterepository = Gmail
   status_backend = sqlite
   
   [Repository Local]
   type = Maildir
   localfolders = ~/Maildir
   
   [Repository Gmail]
   type = Gmail
   maxconnections = 2
   remoteuser = sacha@sachachua.com
   realdelete = no
   folderfilter = lambda foldername: foldername in ['INBOX', '[Gmail]/All Mail', '[Gmail]/Sent Mail', '[Gmail].Starred', '[Gmail].Drafts', '[Gmail].Important']
   nametrans = lambda folder: re.sub('^INBOX$', '[Gmail].Inbox', folder)
   sslcacertfile = /etc/ssl/certs/ca-certificates.crt
   remotepasseval = mailpasswd("gmail")
   

   If you feel comfortable specifying your password in your ~/.offlineimaprc, you can do so by changing remotepasseval to remotepass. If so, you don’t need the pythonfile line.

6. chmod go-rwx ~/.offlineimaprc for a little bit of safety.
7. Type offlineimap to start synchronizing.
8. While that’s synchronizing, use something like this as your ~/.gnus:

   (setq gnus-select-method
         '(nnimap "Mail"
   	       (nnimap-address "localhost")
   	       (nnimap-stream network)
   	       (nnimap-authenticator login)))
   
   (setq user-mail-address "youremail@example.com")
   (setq gnus-ignored-from-addresses "youruser")
   

9. Start Emacs. Start Gnus with M-x gnus. If you don’t see the INBOX group, press ^ (gnus-group-enter-server-mode), open nnimap:Mail, move your cursor to the INBOX, and either press RET to go into the group or press u (gnus-browse-unsubscribe-current-group) to toggle the subscription status until you’re subscribed to the group. Then it should show up on the group screen (M-x gnus).

Hope that helps. Have fun!