Case documentation more sections

Provide section content for

 * Portal
 * Overview
 * Dovecot morals, including namespaces and fs
 * Migrate from OfflineIMAP

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 title: Case of setting up InterIMAP with Dovecot and Mutt for Fripost account on Debian
 ...
 
+This case guide explains the setup of InterIMAP against two separate
+email accounts, e.g. work and private. The guide also covers the
+overview of configuration philosophy and strategy.
+
 *TODO Actually the configuration is for a single account. Restructure
 documentation to cover "single" and "multiple account" setups*
 
 # Overview
 
-Lolcal IMAP servier has a local mail store. InterIMAP works only
-between two IMAP servers. In this case eventually the interest is to
-sync between multiple IMAP servers to cover the case of work and
-private setup.
+A local IMAP server has a local mail store. InterIMAP always
+synchronises between two IMAP servers, *local* and *remote*. In this
+case the goal is to sync multiple remote IMAP servers with local
+ones. And on top of that, configure the mail client with multiple
+accounts.
+
+The following software components are involved:
+
+ * [Dovecot](https://dovecot.org)
+ * [Mutt](http://mutt.org)
+ * [InterIMAP](https://git.guilhem.org/interimap/about/)
+
+The environment is assumed to be Debian Stable, Debian 9 Stretch. For
+InterIMAP, however the Debian Testing repository need to be available.
 
-# Configuration introduction
+The mail client (Mutt) is served via IMAP from a local instance of
+Dovecot. Local storage will be Maildir format. Using the IMAP server
+to serve content to the mail client is preferred, compared to using the
+client's internal Maildir support.
 
-*TODO Fundamental philosophy ...*
+The setup corresponds to multiple running instances of an IMAP server:
+Dovecot is invoked with a separate instance for every client session,
+as well as for the instance of InterIMAP. This is of course no
+problem.
+
+Further, the setup is straight forward. E.g. Dovecot namespaces are
+not needed. Also, all configuration and services are user local. no
+system wide configuration changes will be needed. The system wide
+dovecot service is even disabled.
 
 # Install software
 
@@ -128,6 +153,10 @@ This is standard Systemd configuration. See "systemd.unit(5)".
 
 Stop read here if you are happy with having it all working.
 
+Dovecot has many intricate options for configuration. As explained,
+the setup described in this guide is straight forward. The interested
+can visit the bellow section of comments.
+
 ## Secure your instance
 
 Above configuration assumes that you will disable all of dovecot. As a
@@ -157,4 +186,45 @@ Restart and verify with `ss -ptln` that nothing listens on port 143 or
 
 ## Dovecot namespaces
 
-*TODO Why not ...?*
+Sources
+
+ * Dovecot v2.x
+   documentation, [Namespaces](https://wiki2.dovecot.org/Namespaces)
+
+The benefit of using namespaces is that Dovecot could support
+multiple mailboxes from one instance. Therefore namespaces. would be
+the natural choice for the described setup.
+
+One reason not to use namespaces is that InterIMAP yet doesn't
+support it. However, namespaces would also add unnecessary
+complexity. The setup described here is straight forward. Multiple
+instances of Dovecot does not correspond to a lot of overhead, and
+InterIMAP it would any how causes extra dovecot instances.
+
+## Maildir file system layout
+
+As said, local storage is configured to be in Maildir format. In
+theory Mutt has native Maildir support and could directly parse the
+Maildir folders. Using the IMAP server to serve the content is however
+preferred.
+
+Source
+
+ * Dovecot's
+   documentation,
+   [Maildir configuration](https://wiki.dovecot.org/MailLocation/Maildir)
+
+Dovecot uses Maildir++ directory layout. Folders are prefixed with dot
+(.). There is an option (suffix) `LAYOUT=fs` to enable file system
+layout. We recommend the default configuration. File system level
+management should be treated as dovecot internals, and looked at
+through the IMAP lens, not directly. Also, Maildir++ correspond to a
+clean structure where Maildir's *new*, *tmp* and *cur* folders are
+conceptually separated from mail folders through the naming pattern.
+
+# Migrate from OfflineIMAP
+
+[OfflineIMAP](https://www.offlineimap.org) is a mailbox
+synchronisation solution. In theory one might could reuse a Malildir
+setup from OfflineIMAP. Don't. It is easy enough to re-synchronise all
+email fresh.