PySite is a system to manage and design multiple websites.
It is not a CMS in the traditional sense. Rather, you manage the contents of a website via a filemanager interface, which gives you access to all settings, the pages, the styles, plugins, etc. Compose your pages with Jinja templates, and edit your code comfortably with syntax highlighting in the ACE editor or, wysiwyg style with Aloha.
PySite also contains a facility to manage virtual mailboxes, in case you maintain your own SMTP and IMAP server, e.g. with Postfix and Dovecot. Websites and email domains are independent, so you can host mailboxes for domains that do not have a website, and vice versa.