Modern user interface.
Complete support of IMAP and SMTP protocols including SSL and STARTTLS.
Sieve scripts (Filters and vacation message).
Minimalistic resources requirements.
Direct access to mail server is used (mails are not stored locally on web server).
Allows for adding multiple accounts to primary one, simultaneous access to different accounts in different browser tabs is supported. Additional identities.
Administrative panel for configuring main options.
Really simple installation and update.
Integration with Facebook, Google, Twitter and Dropbox.
Managing folders list.
Simple look'n'feel customization.
Configurable multi-level caching system.
Extending functionality with plugins installed through admin panel.
Perfect rendering of complex HTML mails.
Drag'n'drop for mails and attachments.
Keyboard shortcuts support.
Autocompletion of e-mail addresses.