Cypht for YunoHost
Cypht is a lightweight webmail gathering all your accounts in one place
The driving force behind Cypht development is to provide combined views for multiple accounts, but it's also a standard E-mail client that lets you browse and manage IMAP folders (or POP3 inboxes), and send outbound messages with SMTP.
Cypht is an application built entirely of plugins, or as we call them, module sets (which is obviously way cooler sounding than plugins), that are executed by the framework. Modules provide a flexible way to add new features or customize the program without hacking the code.