The underlying technology that powers business-class messaging (email, calendar, contacts, and tasks) in Microsoft Outlook or its cloud cousin, Outlook Online, is Exchange Online. However, as one of the services in Office 365, Exchange Online delivers more than just messaging. It enables message policies and compliance, encryption, spam and malware protection, and a host of capabilities for workplace productivity. Use this reference to quickly understand the most common business-class messaging features of Exchange Online.

Component Description
Email In the business world, email dominates as the primary means of communication. Email in Exchange Online allows you to sync your messages across multiple devices; when you reply to an email from your mobile device, you see the same reply on your desktop application.
Calendar A calendar in Exchange Online not only allows you to store appointments and set up meetings, but it also displays "free/busy" information for people in your organization. Setting up meetings becomes less cumbersome since the "free/busy" information shows the availability of the meeting participants.
Contacts Having a place to store all of your contacts is critical in today's connected world. With Exchange Online, company contacts are stored in the Global Address List (GAL). The GAL allows you to access, directly from the Outlook desktop application or from Outlook Online, information about people such as organizational hierarchy, availability, and even email statistics of your interaction with them.
Tasks In today's "always on" world, it's easy to get distracted and end up doing many things without accomplishing much at the end of the day. Tasks in Outlook allow you manage your To Dos, set flags and reminders, define categories, and even assign a task to someone else and track its status. Just like the other features in Outlook, tasks can be synced to multiple devices and integrate with native task applications for mobile devices.