Some common reasons organizations choose Zimbra over Fusemail.com include:

1. Free/busy time scheduling
2. Delegated sharing and syncing shared resources like calendars and contacts
3. Native Mac mail, ical and addressbook sync (Tiger and Leopard)
4. Thunderbird drag and drop and sync mail, calendars and contacts
5. Mobile device over-the-air (OTA) sync, including iZimbra for the iPhone

The following feature comparison is based on research as of March, 2008. We welcome your comments and suggestions to improve this table. Please note that we have listed current features, so this table will change as new features are released. Also note that this is not a strategic comparison. 

Features	01.com Zimbra Hosting	Exchange Hosting
Recurring Fees	$4.99/user/mo for Business	$.99/user/mo (min $10 or $100/mo)
Maximum Number of Mailboxes	Unlimited.	Unlimited.
Bring Your Own Domain Names (yourcompany.com)
Domain Admin / User Provisioning & Management
Maximum quota (GB/mailbox)	Unlimited (Extra fees)	Unlimited (Extra fees)
Maximum attachment message size (MB)	50	50
Data Portability (move your data to another solution)	Open-standards based.	Proprietary.
Secure LDAP Information Lookup (Mail.app, Outlook, etc.)
24/7 live support for Mac and Windows users	Included for every person with a mailbox.	With branding, only for 1 admin.
Mail folder sharing		Limited. (not delegated)
Secure Chat	(beta)	Jabber only (security?)
Off-line access in web-browser
CalDav & WebDav compliant
File sharing (including drag and drop to web!)		(FTP only)
Task list delegation/sharing		Sharing only.
Branding - Custom Logo	Free.	Limited. Extra fees.
Wiki / Document Sharing
Calendar sharing & delegation		Sharing only.
Contact sharing & delegation		Sharing only.
Global Address List (GAL/LDAP) - Company Address Book	Included.	Included.
Free/busy checking for group calendaring	Included.
Resources (IE: conference rooms, projectors)
LDAP - Open/Active Directory Integration	Built-in, optional.	API's available.
Instant, Self-Activation/Cancellation		Activation only.
Advanced, Personal Anti-Spam/Anti-Virus	Included. Or use your own.	Included.
Desktop Sync Support (Outlook, Mail, iCal, AddressBook)	Mac, Linux & Windows.	Outlook only.
Blackberry OTA sync (email, calendar, contacts)	Native BES (beta).	Additional software.
Free iPhone Support	(IMAP & iZimbra).	IMAP only.
Windows Mobile & Palm sync (email, calendar, contacts)	Optional.	Web browser only.
Web 2.0 Mash-up framework (Zimlets)	Included.	Limited.
Web Identities	Included. (+Sync to Outlook)	Included. (web-only)
Terms	Monthly. Cancel anytime.	Small biz: Monthly. Cancel anytime. Large biz: annual.
Service Level Agreement (SLA)	99.975%	99.95%
External POP/IMAP - Email account centralization
Distribution Lists (mailing lists)	Unlimited & free.	Unlimited & free.
Aliases	Unlimited & free.	Unlimited & free.
Optional "free" version with Ads and no 24/7 support.
Software as a Service (SaaS)
May be redeployed in-house, on your own servers.
Mining user data and other info (see privacy)
Keyboard/navigation short-cuts
Published Road Map		Limited.
Able to restore deleted message (rollback)	30 days.	10 days
SOX Compliance (Archiving & Discovery)	Optional. Built in!	Limited archiving only.
Free Trial	30 days	7 days