New features introduced in Exchange Server 2016

New features in Exchange Server 2016

• Combine Roles: A reduction in the number of available roles to two: a Mailbox Server and an Edge Transport (intended only in certain Office 365 hybrid scenarios). 
• Outlook on the web (formerly Outlook Web App): UI changes 
• Office 365 hybrid: The Hybrid Configuration Wizard (HCW) that was included with Exchange 2013 is moving to become a cloud-based application. When one chooses to configure a hybrid deployment in Exchange 2016, you'll be prompted to download and install the wizard as a small app. 
• Messaging policy and compliance: New DLP and Archiving/Retention/eDiscovery features. 
• Improved download package Exchange 2016 releases, starting with CU1, are now packaged as ISO files instead of a self-extracting EXE file. The ISO file can be mounted directly in Windows Server 2012 or later. If you need to install Exchange across a network, you can create a network share from the mounted ISO drive.
• MAPI over HTTP is now the default protocol that Outlook uses to communicate with Exchange. MAPI over HTTP improves the reliability and stability of the Outlook and Exchange connections by moving the transport layer to the industry-standard HTTP model.
• Document collaboration: Exchange 2016, along with SharePoint Server 2016, enables Outlook on the web users to link to and share documents that are stored in OneDrive for Business in an on-premises SharePoint server instead of attaching files to messages. Users in an on-premises environment can collaborate on files in the same manner that's used in Office 365.
• Public folder support for In-Place eDiscovery and In-Place Hold
• Compliance Search:no limit on the number of mailboxes that can be included in a single search,There's also no limit on the number of searches that can run at the same time,in Exchange 2013: you can search up to 10,000 mailboxes in a single search and your organization can run a maximum of two In-Place eDiscovery searches at the same time.

For more detail on new features, see the following Microsoft TechNet article: Whats new in Exchange 2016