- Spell checking (squirrelspell)
- Mail filters (filters)
- Web-based administration of SquirrelMail (administrator)
- A calendar (calendar)
- An interface to submit bug reports semi-automatically (bug_report)
Examples of functionalities added by various third-party plugins include:
- Address book/contact grouping and other address book expansions
- Monitoring and security tools to track usage, fight attackers and improve security
- Password change
- Quota reporting
- Rich text (HTML) email composition and display
- User-configurable front-ends for autoreponders, spam filtering systems such as SpamAssassin and server-side mail filters
- Weather reporting