My No. 2 pick is the improved storage reliability. This lumps together several discrete enhancements, but the short story is that you can now run Exchange reliably without dealing with Windows clustering, RAID arrays, or fancy Enterprise-class disks. It'll be cheaper to store mailbox databases and faster to recover mailboxes in the event of failures.
My No. 3 pick is MailTips. Are you about to accidentally send a personal e-mail to the whole company? A a time-sensitive e-mail to someone who is on maternity leave for six months? A 30MB attachment to people who have 20MB attachment size limits on their mailboxes? MailTips tells you before you send the message.
And my No. 4 pick is conversation view. Have the arrangements for a company party Friday night cluttered up your mailbox to the point where you can't find the approval e-mail for the urgent customer visit that you need to book today? Switch to conversation view, and collapse those 50 party discussions into one expandable node. This isn't a new idea; we were doing threaded conversations on bulletin board systems 25 years ago. But it is new to Outlook and OWA, and it's more than welcome.
New in Microsoft Exchange Server 2010
OWA (Outlook Web Access) support for Internet Explorer 7 and 8, Firefox 3, and Safari 3
Reply/forward status maintained by server, displayed by all clients
Warn about large distributions, out-of-office recipients, etc.
Message threading; reduces mailbox clutter
Calendar sharing extended to OWA, federated users
Extend shared contacts beyond organization and desktop
Voice Mail Preview
Automatically transcribed text-based preview of voice mail messages
Call Answering Rules
Incoming phone calls managed like incoming e-mails
Rights-management in OWA
Read and create IRM-protected messages natively in OWA as well as Outlook
Trust Exchange servers of partner organizations, share calendars, presence
Automatic repair of corrupted database pages from copies
I/O bursts reduced, allowing use of SATA (desktop) disk drives
Replicated mailbox databases allow use of JBOD (concatenated disks) instead of RAID arrays
Database availability groups
Redundant copies of mailbox databases with continuous replication, automatic recovery
Removes need for clustering, improves overall uptime
Online Move Mailbox
Mailboxes can be moved during normal business hours with user online
Transport protection rules
Allow an administrator to automatically apply IRM protection to e-mail after sending
Re-direct mail to a manager or trusted moderator for review, as a transport rule
Outlook protection rules
Automatically triggers Outlook to apply an RMS template to a message before it is sent
Role-Based Access Control
Delegation of specific authorities simplifies administration
Exchange Control Panel (ECP)
User self-service for tasks that used to require administrators
Users can track message delivery without a help-desk call
Distribution group management
Users can create, manage, and moderate distribution groups
Mobile Device Block/Allow List
Administrators can select which devices can sync data
Protected voice mail
Prevent voice mails from being forwarded outside the organization
Move PST files to a secondary Exchange mailbox for performance and compliance
Cross-mailbox search user interface for HR, compliance; does not require administrator
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