Roundcube

Roundcube is a browser-based IMAP email client designed to provide a full-featured webmail experience on top of existing mail servers (IMAP/SMTP). It focuses on a clean UI, standards-based email handling, and extensibility via plugins and skins.

Key Features

• IMAP webmail UI with message list, conversation-style viewing, and folder management
• SMTP sending with support for multiple sender identities and per-identity settings
• Address book with groups and LDAP integration via plugins (commonly deployed)
• Powerful search and message filtering capabilities (server-dependent; supports standard IMAP search)
• MIME and HTML email rendering with attachment handling
• Sieve / ManageSieve integration via plugin for server-side mail filtering rules
• Extensible architecture: plugin API, skinning system, localization, and theming
• PGP support available through plugins (e.g., Enigma/PGP-related plugin ecosystems depending on deployment)

Use Cases

• Provide webmail access for a Postfix/Dovecot-based email domain without outsourcing to hosted webmail
• Offer a lightweight, user-friendly mailbox interface for small organizations, ISPs, and homelabs
• Add server-side filtering (Sieve) management to an existing IMAP service via plugins

Limitations and Considerations

• Not a full groupware suite by default; calendars/contacts sync and advanced collaboration typically require plugins and/or external services
• Feature depth depends on IMAP server capabilities and installed plugins (e.g., Sieve, LDAP)

Roundcube is a mature, widely deployed webmail client that integrates with standard mail server stacks. Its plugin and theming ecosystem makes it adaptable for many email hosting scenarios while keeping the core focused on webmail.