Roundcube webmail...

...is a browser-based multilingual IMAP client with an application-like user interface. It provides full functionality you expect from an email client, including MIME support, address book, folder manipulation, message searching and spell checking. More information

Features

Drag-&-drop message management
Full support for MIME and HTML messages
Multiple sender identities
Full featured address book with groups and LDAP connectors
Find-as-you-type address book integration
Threaded message listing
IDNA and SMTPUTF8 support
Spell checking
Responsive skin (multi-device support)
Shared/global IMAP folders
Support for access control lists (ACL)
Built-in caching for fast mailbox access
Unlimited users and messages
Import/export functions
Plug-in API for flexible extensions
XSS attack protection
Support for PGP encryption

Complete list of features