| Zimbra Desktop | Microsoft Outlook | Mozilla Thunderbird | |
| Cross Platform | Microsoft Windows, Mac OS, Linux | Microsoft Windows Only | Microsoft Windows, Mac OS, Linux and more |
| Cost | Free | Commercial License | Free |
| Open Source | 100% | No | 100% |
| Support Enterprise Collaboration Server | Zimbra Collaboration Server | Microsoft Exchange Server | No |
| Identical UI as Enterprise Collaboration Server Web UI | Yes | No | No |
| Integrated Calendar | Yes | Yes | Via Lightning extension, beta version |
| Corporate Address Book | Yes | Yes | No |
| Briefcase | Yes | No | No |
| Tasks | Yes | Yes | Via Lightning extension, beta version |
| Groupware Sharing and Delegation | Yes | Yes | No |
| Gmail Mail Support | Yes | Yes | Yes |
| Google Address Book Support | Yes | No | No |
| Google Calendar Support | Yes | No | No |
| Yahoo! Mail Support | Yes | No | Via WebMail extension, not production quality |
| Yahoo! Address Book Support | Yes | No | No |
| Yahoo! Calendar Support | Yes | No | No |
| POP3 Support | Yes | Yes | Yes |
| IMAP4 Support | Yes | Yes | Yes |
| Cross-account Message View | Yes | No | No |
| Cross-account Calendar View | Yes | No | No |
| Cross-account Address Book | Yes | No | No |
| Email Address Auto Complete | Yes | Yes | Only previously mailed contacts |
| Drag and Drop from Desktop | Yes | No | No |
| Support Tagging All Data Types | Yes | No | No |
| Conversation View Across Folders | Yes | No | No |
| Usable When Offline | Yes | Yes | Yes |
| Seamless Online/Offline Transition | Yes | Yes | No |
| Access All Data Offline | Yes | Does not download all data by default | Does not download all data by default |
| Manage Multi-GB Mailboxes | Yes | Slow | Slow |
| Search across Multi-GB Data | Index based, fast | Limited and slow | Limited and slow |
| New Mail Notification | Yes | Limited | Limited |
| Themes and Colors | Yes | No | Yes |
| Auto Update | Yes | Yes | Yes |
| Extensibility | Zimlets | Plugins | Extensions |