This step is optional but most email service providers offer their users a way to read emails in a browser. Luckily this is easy. The package you need is called "squirrelmail" - a web mail system that can use any IMAP server - just like the Dovecot IMAP server we use here. To set it up you first need to add its configuration to your Apache configuration:
$> ln -s /etc/squirrelmail/apache.conf /etc/apache2/conf.d/squirrelmail.conf $> apache2ctl restart
You need to change one configuration option at least so please run the configuration utility:
Select option 3 (Folder Defaults) and set option 1 (Default Folder Prefix) to 'none'. You may also want to browse through the other menu options to e.g. set your organisation's name right.
Point your browser at http://YOUR-MAIL-SERVER/squirrelmail and you should see the webmail interface. Login as 'email@example.com' with password 'summersun' and you should be able to read John's email. It couldn't be simpler.
In case you are unhappy with the http://my.server/squirrelmail URL and prefer to use http://my.server instead you should read the users will prefer a simple URL section in the /etc/squirrelmail/apache.conf file.